However getting anything like a gig over more than 20 meters will be fun.
If using cheapo switches with gig uplinks then you will be lucky to get more than 150 - 200 over that kind of distance. I use 3com 4900 series switches and have seen 800 over 40 meters, if you bind them up and use a couple together then you get some reasonable throughput.
Have you thought about fibre ?