I would stay away from aluminum and get vinyl screening. They sell kits (with framing for windows) or by the roll. Really easy to work with . . .
Just keep in mind "easy cleaning" when you design your cage.
If you have the cage full of plants, they will catch and absorb most of the water from misting. Since you are building a cage, you can add a drain on the bottom. This way you can still use your matting. Also, if you intend on using either some sort of dripper, you can always place a cup underneath where the water will land and change it out every day. The big problem with standing water is when people do not clean it out every day. (BTW: an ice cube left on top of the screen top makes a great little dripper!)
Veileds are pretty hardy but try to get a basking temp in the high 80's low 90's. For me that was a 75w incandescent bulb. They thermo regulate rather well on their own.

You CAN spend a lot of cash on accessories so that is totally up to you. Understand the husbandry and you can get by with many DIY items.

I agree with the other poster. You can get very healthy animals from reputable breeders that ship overnight. I have never had a problem. Will cost about $50 extra but well worth it. If you do try to find something locally just make sure it is not dehydrated (sunken eyes/Dark skin around the eyes) or weak. I know these are obvious points but sometimes overlooked when excited about getting a new animal! ** And make sure you get a male!

Jim