Check this article out.

http://www.qsl.net/n9zia/wireless/pd...ug1998-p64.pdf

It's an article about making a shielded room from foil covered foam board.
You'd still have the problem of getting your power in, and signal cable out.
Actually, the signal cable out would be fairly easy. Bulkhead mounted
type-N or SMA connectors are made just for that purpose. The power would be
slightly more difficult. Not only do you want to keep stray RF from leaking
through the hole, but it would require filtering to reduce conducted noise
on the lines also. One of my first real jobs was at an commerical two-way
dealer. The shop, and tower were really close (less than a mile) to a 50 kW
AM broadcaster (WTOP 1500 kHz). Guess how I discovered 60 volts AC between
the cases of two AC outlets. I also learned that a 3 dB reduction in
reciever sensitivity makes a big difference, but reducing the noise level by
3 dB doesn't.

Come to think of it, of all the screen rooms, and sheet metal shielded rooms
I've ever been in the biggest problem was ventilation.

Robert N3LGC