I just recently got four sugar gliders off Craig's list. They came with a cage that is roughly 3 1/2' tall, 2 1/2' long, and 1 1/2' wide. I found a website saying that is enough space for three to four, but I was wondering if that really is or not. I also wanted to know that if I rescued four more sugar gliders, and they were all willing to make peace and share a cage, how big would the cage need to be to house eight? Thank you.

Your current cage is way too small for four gliders! Take a look at this setup by Minnesota Zoo (one of the forum members).

http://www.sugarglider.com/glidergossip/topic.asp?TOPIC_ID=49994

What size do you think I would need for eight gliders? I was looking into buying or making one that is 30" wide, 48"long, and 72" tall. Do you think that would work?

Honestly I don't know! When you get your other gliders you will need to keep them separate for a 30 quarantine period while you get them tested for parasites, so you will need multiple cages. Hopefully someone here with a larger colony can help you with cage sizing.