Brad,
Try this topic:
http://www.dendroboard.com/phpBB2/viewtopic.php?t=5450
Basically here are your requirements:
1. Allows light to pass through (up to you if its UV or not)
2. Allows for some sort of access (usually means two parts)
3. Allows whatever ventilation you want
4. Allows cords and plumbing in and out if required
5. Weight bearing if you will put light or other stuff directly on top of it
Glass
Pros:
Pretty easy to get custom cut
Doesn't warp or bend
Holds in moisture well
Cons:
Can break
Doesn't pass UV light (unless you get quartz $$$$)
Hard to drill for cords, etc
Acrylic Plexiglas, Acrylite (etc)
Pros:
Pretty easy to get custom cut
Easy to drill
Holds in moisture well
Can be UV transmitting
Cons:
Can warp or bend
Pretty hard to get scratches out
Can yellow or age
May be harder to find
Screen
Pros:
Easy to make yourself
Allows great ventilation
Passes some UV through
Cons:
Probably not enough moisture retention (some use saran wrap to help)
Not very load bearing
True FF proof screen can be expensive or hard to find
It seems most use either all glass cut in sections to allow access, glass and screen, or acrylic and screen.
You can see what I did in the thread above.
Best,
Marcos