Here is a State Forest map that includes Cooks Forest State Park to get you started:
http://www.dcnr.state.pa.us/forestry/stateforests/clearcreek/maps/index.htmThe River Road, upstream from Cooks Forest SP is pretty nice road ride along the Clarion River. There are free, Allegheny National Forest campsites in the Belltown/Millstone area... I suspect they are hard to get in the summer season.
I think, way back, I did my first overnight bike trip with my buddies when I was 18 or 19. We had a blast on that trip...
Another alternative, is to do a section the Great Allegheny Passage.
Have fun.