-Where to find Rubbermaid containers (sterilites too)-
Target
K-mart
Wal-Mart
The Container Store
Bed Bath and Beyond

How to make the cover-
Buy the top

Ventilation-
Get a soldering iron or a hot glue gun (if hot glue gun take all glue out) and melt about 10 holes on each of the "short" sides of the container about 3" above the bottom or if you will be using a particle substrate 2" above the substrate level (keep it low, at the top kills heat and humidity).

Heat-
Use Heat pads. I suggest either a human heat pad with low, med, high settings (keep it on low) or The T-rex, Ultratherm, or Four paws (the only one i’ve used, runs at 95 degrees) brand reptile heat pad. If you do buy a reptile heat pad DO NOT attach it to the container. Get a thin piece of cardboard (the box it came in folded flat) and attach it to that. Then place the heater under the cage and it will not run as hot and be more effective.

Why not Aquariums-
Ball pythons are small, shy, and secretive snakes. Their favorite thing to do (after being adjusted to a new cage) during the day is to hide. Very rarely have I seen my ball python out during the day (except right when i turn the lights on, but that is right after night so it doesn’t count) it is usually feeling comfortable in one of its terra-cotta hides. Ball pythons like "dark" containers they do not like being in light (take your ball python outside on a sunny day in the summer and it will try to find shade) they like it when it is semi-dark to dark (they can hide better).

Aquariums are made out of glass, a material that defines insulation at its worst. Glass heats up and cools down extremely quickly. When kept in a cool room it does not hold heat good at all. Glass aquariums also have bad ventilation, in this case ventilation at the top. The top ventilation combined with how hot air rises and how humidity is the amount of moisture in the air makes for a cool dry cage. The hot humid air rises straight out of the cage and into no where land leaving you with a dry cage. The top ventilation combined with a heat lamp make it even worse. The heat lamp heats the air (as opposed to objects) and makes it rise even faster makeing more heat and humidity escape.

Pros of Aquariums-
You can see in it perfectly (how does that help the snake?)

Cons of aquariums-
Made of glass
Allows tons of light in
Top ventilation
Heavy
Hard to keep heat and humidity in
Annoying to clean (stupid streaks....)
Expensive (when compared with its quality and price of other cages)

Pros of plastic (rubbermaid/sterilite) containers-
Holds heat and humidity well
Can control the ventilation
Allows little light in
You can see in it (quite easily, just a little darker and "blurry" IMO)
Light weight
Easy to clean
Racks...
Come in lots of sizes and are CHEAP
Usually on sale at one store

Cons of Plastic containers-
You can’t see in it as good as aquariums