Hello,
It sounds like your typical Revit file can range from 20-30MB on the low end, up to 75-100MB for larger projects. Low end for example is a 4500 sq. ft. classroom building we did. I did make a small model of part of a central utility plant we were installing a new surge tank in and that was 8MB just for some pipes, pumps, and a few walls. Keep in mind that those larger projects are about 75-100MB per file (i.e. MEP, Arch, Struct). Plan to use an ftp site or send CDs to/from clients if want to dive into the Revit pool. A decent internet connection can't hurt either.
Hope that helps,
Joe
Joe Fields PE, LEED AP BD+C
Mechanical Engineer and C# Enthusiast