A terrarium is a glass enclosure, like an aquarium, but for reptiles. It should include a mesh lid. The minimum gallon size for a ball python is a 40 gallon, though you can go smaller than that, but it is not recommended. A 40 gallon allows the snake to stretch out and explore better than what it could in a 20 gallon. 

Plastic tubs/bins can also be use, though I personally do not like using them for ball pythons. But this is also an option instead of a super expensive terrarium. It can be temporary, so if you're saving up for a terrarium, it is ok to use a plastic tub/bin in the meantime. Plastic bins/tubs tend to hold humidity quite well, and humidity is something ball pythons need. Plastic bins/tubs are an ok option, but in my opinion terrariums are a bit better, as they look nicer, and are usually larger. Make sure the plastic tub/bin can fit AT LEAST two hides and a water dish, if it cannot than find a larger tub/bin. They also require cleaning more often as they hold bacteria easier. 

Lighting, so light bulbs (Ensure they are NOT ordinary light bulbs, use reptile bulbs.) an 80 watt or 100 watt should keep your snake hot enough. I suggest a big round dome, that you put the light bulb in, and a smaller dome that you can put a lower watt night bulb in, such as a 50 watt or 60 watt. Night bulbs are a little controversial in the reptile world, they can cause blindness in bearded dragons apparently. I personally use a black light 60 watt night bulb for night. It helps keep the heat up. However if your UTH (under tank heater) is good enough you may not need a night light. I suggest a UTH large enough to AT LEAST cover the area of the warm hide. 

Here's the link to the bulbs I use

US- 100 watt-   https://www.amazon.com/Zoo-Med-Repti-Basking-Replacement/dp/B07RYNKCQ3/ref=sr_1_8?crid=P1A8X55WRXSJ&keywords=80+watt+zoo+med+bulb&qid=1663799443&sprefix=80+watt+zoo+med+bulb%2Caps%2C151&sr=8-8

75 watt- https://www.amazon.com/Zoo-Med-Repti-Basking-Replacement/dp/B07SG7C5VC/ref=sr_1_7?crid=P1A8X55WRXSJ&keywords=80+watt+zoo+med+bulb&qid=1663799489&sprefix=80+watt+zoo+med+bulb%2Caps%2C151&sr=8-7

Canada- 100 watt pack of 4-  https://www.amazon.ca/Zoo-Med-Repti-Basking-Spot/dp/B07PJV8XYJ/ref=sr_1_1?crid=3C6TFGCZZ3A08&keywords=zoo+med+bulb+100+watt&qid=1663799599&sprefix=zoo+med+bulb+100+wat%2Caps%2C115&sr=8-1

75 watt pack of 4-  https://www.amazon.ca/Repti-Basking-Lamps-Watt-Pack/dp/B01BIC0PJO/ref=sr_1_8?crid=2YS3XM69T77P5&keywords=zoo+med+bulb&qid=1663799641&sprefix=zoo+med+bulb%2Caps%2C275&sr=8-8

I could not find the black light bulbs I use, but they do have them in stock at most pet stores that sell reptiles. A red night bulb could be used, but I prefer black lights. 

UTH(Under tank heater) I use

US-  Small UTH-   https://www.amazon.com/Zilla-Reptile-Heating-10-20-Gallon/dp/B002Z5GOU8/ref=sr_1_27?crid=303EFGVJWGHVB&keywords=under+tank+heater+for+reptiles&qid=1663799775&sprefix=under+tank+heater%2Caps%2C194&sr=8-27

Large UTH-  https://www.amazon.com/Zilla-Reptile-Heating-10-20-Gallon/dp/B002Z5GOU8/ref=sr_1_27?crid=303EFGVJWGHVB&keywords=under%2Btank%2Bheater%2Bfor%2Breptiles&qid=1663799775&sprefix=under%2Btank%2Bheater%2Caps%2C194&sr=8-27&th=1

Canada-  small UTH pack of 2-     https://www.amazon.ca/Reptile-Heating-Pad-Terrarium-Heater/dp/B07X5SW64Y/ref=sr_1_6?crid=2U28DH3RYNP8E&keywords=under+tank+heater+reptile&qid=1663799878&sprefix=under+tank+heat%2Caps%2C116&sr=8-6

Let's talk about heater rocks. 

These can severely burn your ANY reptile, including ball pythons. If you really want one I suggest wrapping it in a hand towel or reptile hammock so that the animal is not sitting directly on the heat rock. Overall I just don't recommend these, but it's your choice. They also range from $25 USD, to $35 CAD. 

Domes I use

US- Large dome can withstand a 150 watt bulb-  https://www.amazon.com/Zilla-Premium-Reflector-Dome-Black/dp/B005OCWP1Q/ref=sr_1_7?crid=2BY0KJUTE9VZN&keywords=reptile%2Blight%2Bdome&qid=1663800104&sprefix=reptile%2Blight%2Bdome%2Caps%2C187&sr=8-7&th=1

Small can withstand 60 watt bulbs-  https://www.amazon.com/Zilla-Premium-Reflector-Dome-Black/dp/B000TZ1XH0/ref=sr_1_7?crid=2BY0KJUTE9VZN&keywords=reptile%2Blight%2Bdome&qid=1663800104&sprefix=reptile%2Blight%2Bdome%2Caps%2C187&sr=8-7&th=1

Canada- Big dome-  https://www.amazon.ca/Zilla-Premium-Reflector-Dome-Black/dp/B005OCWP1Q/ref=sr_1_11?crid=11TP5IOLJ2XY3&keywords=reptile+light+dome&qid=1663800174&sprefix=reptile+light+dome%2Caps%2C146&sr=8-11

Small dome-  https://www.amazon.ca/Zoo-Med-Fixture-5-5-Inch-Black/dp/B002OVDPJQ/ref=sr_1_11?crid=11TP5IOLJ2XY3&keywords=reptile+light+dome&qid=1663800209&sprefix=reptile+light+dome%2Caps%2C146&sr=8-11

Usually reptile supplies are cheaper on Amazon then buying in store, so Amazon might be your friend when it comes to reptile supplies.

Now for hides/huts, these are what your snake hides in or sleeps in, or just lazes about in. You need two hides per snake. A warm side hide. Your warm side by the way is where the main basking light is, I put mine on the left side. This hut is where your snake goes to keep warm. You also need a cold side humid hide. The humid hide needs to be humid, you can achieve this by putting sphagnum moss in it and misting it daily, or by getting a literal hide made of moss and misting it. 

US- warm hide-  https://www.amazon.com/Leoterra-Reptile-Lizards-Leopard-Material/dp/B08KG4HMN5/ref=sr_1_7?crid=3R2NOCVS5DVFV&keywords=snake%2Bhide&qid=1663800525&sprefix=snake%2Bhide%2Caps%2C191&sr=8-7&th=1

Also that is quite a big hide, make sure it will fit your enclosure!

Humid hide-  couldn't find it on Amazon US. But you can use the same hide as above, or another one that is big enough, and fill it with sphagnum moss.

Sphagnum moss-  https://www.amazon.com/Zoo-Med-Laboratories-SZMCF3NZ-Sphagnum/dp/B0035Q4CVE/ref=sr_1_2?crid=ECHQCO50GHY7&keywords=sphagnum+moss+for+reptiles&qid=1663800685&sprefix=sphagnum%2Caps%2C139&sr=8-2

Canada- warm hide-  https://www.amazon.ca/Leoterra-Reptile-hideouts-Different-Material/dp/B08KG4HMN5/ref=sr_1_5?crid=5Q88PMZJE4P3&keywords=snake+hide&qid=1663800716&sprefix=snake+hid%2Caps%2C181&sr=8-5

Again a quite large hide, be sure it will fit your enclosure

Humid hide-   https://www.amazon.ca/kathson-Reptile-Humidity-Hideout-Chameleon/dp/B07YDF5GRG/ref=sr_1_2?crid=198J2R8ZJ1DGC&keywords=snake+humid+hide+moss&qid=1663800805&sprefix=snake+humid+hide+moss%2Caps%2C106&sr=8-2

This humid hide will be too small for an adult ball python, but is good for juveniles.

Sphagnum moss-  https://www.amazon.ca/Zoo-Med-Laboratories-Sphagnum-0-33-Pound/dp/B0019J2MA2/ref=sr_1_3?crid=1ZLZVOSWQQBA8&keywords=sphagnum+moss+for+reptiles&qid=1663800881&sprefix=sph%2Caps%2C143&sr=8-3

A large brick of moss.

Accessories. Though not necessary, they are nice for your ball python to have, and nice for you to look at. Some accessories I like:

Note these links are Amazon Canada

Leaves-     https://www.amazon.ca/Reptology-Climber-Reptile-Terrarium-12inch/dp/B06X9H68NL/ref=sr_1_7?crid=1A9XJ4F8DE14L&keywords=terrarium+accessories&qid=1663800958&sprefix=accessories+for+terr%2Caps%2C157&sr=8-7

Water dish-     https://www.amazon.ca/Exo-Terra-Corner-Pebble-Water/dp/B07WFPPFNJ/ref=sr_1_18?crid=1A9XJ4F8DE14L&keywords=terrarium+accessories&qid=1663801037&sprefix=accessories+for+terr%2Caps%2C157&sr=8-18

Now moving on to water dishes, yes snakes need water. I suggest a water dish large enough for the snake to soak in, but a smaller dish can also be used. You can even use dog water dishes. I like my large Zoo Med ones though. 

Bedding/substrate. Important, more important than you may think. I do not recommend sand, it can cause impaction, and impaction leads to death of the animal, so just avoid sand. The bedding I like using is Zoo Med Forest Floor, or Peat Moss. Zoo Med Forest Floor can be found at most pet stores that sell reptiles, and can be found on Amazon. Peat Moss is amazing at holding humidity, and can be found in large quantities for a decent price at most hardware stores and plant stores. In Canada peat moss usually goes for $25, so in US I estimate around $19. 

Canada- Forest Floor-   https://www.amazon.ca/Zoo-Med-Forest-Bedding-8-Quart/dp/B001OVF6Z8/ref=sr_1_2?crid=3PTLYEJJ0AII2&keywords=jungle+floor+bedding&qid=1663801282&sprefix=jungle+floor+bedding%2Caps%2C150&sr=8-2

US- Forest Floor-   https://www.amazon.com/Zoo-Med-Forest-Floor-Bedding/dp/B0010OVM7A/ref=sr_1_4?crid=N8NYBOF1YPNQ&keywords=forest%2Bfloor%2Bbedding&qid=1663801338&sprefix=forest%2Bfloor%2Caps%2C132&sr=8-4&th=1

You also need a temperature gauge, and a humidity gauge. These will tell you the temperature of your terrarium. While a humidity gauge will tell you the humidity. Temperature for ball pythons hot side should be 80 to 90 degrees Fahrenheit, or 30 to 35 degrees Celsius. Humidity should be AT LEAST 70%, though 80% is more recommended. Gauges can go from anywhere $5 CAD to $20 CAD. $5 USD to $15 USD. You will need two temperature gauges, one for warm side, one for cool side. Same goes for humidity gauges. Cool side temperature should be around 60 to 75 degrees Fahrenheit, or 20 to 25 degrees Celsius. Humidity in the cool side is usually higher than the hot side, usually around 80%, while the hot side being 75%.