Building a JCP enclosure, Please help.

[Xanafein]

I Am currently keeping my 4 month old JCP (sweetheart) in a 25 gallon tank with a mesh top with some plywood on top to hold in humidity and heat, however, she is growing fast, and it is nearing the time to get her a better more permanant home, i work a crappy job making minimum wage, and dont have the extra cash to buy a large home for her, wich brings me to my quandry, how to build her new home, since she is going to end up being a 7 foot snake, im looking at a cage with the following dimensions, following this order Hight x Depth x Length

4.5' x 2 'x 4'

givving 8 square feet of floor space, and 4.5 feet of up room, that being said i need to look into materials and such, any tips would be much apreciated, she will be fine in her 25 gallon for at most 3-4 months, after that, she could live in it but i doubt she would be comfy