Be careful doing that.. I built my first cage because I had some thoughts that I would save money. After I screwed up several times, I discovered I would have saved frustration and money if I had just purchased one. If you plan to build one, do it because you have an idea of how you want it, not to save money. It doesn't usually work.
They sell reptariums at lllreptile. Good prices too. The 175 gallon would be your best bet as far as sizing goes you could probably get away with 100 gallon. They run from $60-75 for these two sizes. The link is on the front page. Some people complain about them but really you will have the same worries no matter what screen type cage you go with.
If your dad and you did get ambitious you can put one together for close to the same price as long as everything goes good. At Home Depot, Lowe...etc. they sell window/door screening stuff. You can buy the metal framing and cut to the sizes you need. They sell "T" end pieces which make the put together a little easier. The screen and spline. You will have to get creative as how you are going to put the bottom together. Hardware to secure the sides, hinges for the door, and some sort of lock for the door. For everything you are going to but it will run you in the neigborhood of $70-80.
I like the reptarium option better. If you keep checking in with lllreptile the run specials some times and these cages get real cheap. www.lllreptile.com
The link is also on the front page if you want to check back. They sell these at the pet stores in my area but are almost double the prices it maybe the same where you live.
I hated the reptariums cause they took longer to clean and crickets would chew holes in that fabric screen but if you only have one cage to clean it probably wont bother you .I have 10 to clean and i needed something convient.
well i could probobly make it my own ill look into the reptariums, but it would be easy cause im very good at making things like that i take woods and medal classes in school. and my dad is good at that stuff to so plz post some directions anyway
www.cages.net will make you a cage to your size and cost about the same as LLLreptile. I got mine from there and could not be happier. I had them make it to the size of a plastic tote. I got that to catch water and I drilled a hole in it to drain the water out. I fits in there like a glove and I have a mister going nothing drips out.
BTW The plants have grown in now. He has lots of places to hide.