Bob's right, David. You can start with most any old bike (obviously a chopper won't be easy w/o cutting frame. etc). Old standard bikes are good starts. Then just strip it, slap some clip-ons on the thing (or something that makes you ride forward and low), cut the pipes (make it loud) then go get some old leathers
. CB's are probably most common cafe racers since there are lots of shops making stuff for them...(a chicken and egg thing really). They don't have to be big bikes to be fun. I've had an 80cc and a 250cc motorcycles before, and I probably had more fun tearing around on those.