How big of habitat do I need? Should it be tall, long or wide? Should it be made of glass, wood, screen or wire mesh?

To answer these questions you need to know your pet. How big will it get? Does it like to climb, run or hide? How active it is? How warm does it need to be? What level of moisture does it need?

Active animals need room to move. Vertical or Horizontal they need a larger area than one that just hangs out all day or stays hidden except to eat. A larger basking animal many be fine in a habitat that is to confined for a smaller active animal. As a general rule arboreal need height were as terrestrial need length.

What it is made out of depends on how warm you need to keep it and how high the humidity has to be. Screen provides a lot of air movement and glass holds moisture. It also depends on how your animal gets around and how large it will become.