I changed trucks recently and need to build a boat rack on an older F150, I work in metal fabrication so Im not limited by much as far as building it goes. I know theres racks out there with rollers for loading small boats but Ive never seen one up close, I have a canoe but want to build the rack heavy enough for small boats because I'll likely sell it once I find a topper I like, if anyone has something I'd appreciate some detailed pics. TIA

Remember the late 70's through to mid 80's fullsize jimmy's and rams had an inside rollbar?  I just got one from a wrecker;  had to slightly twist and bend the legs to be the right width/angle, but their mounting plates re even pre drilled for bolts.   

I just bolted it to the inside lip of the truck box.  Contact cemented some carpet on the horizontal pieces for slides.  Works great.  12' johnboat hangs over the cab sufficiently to strap it down to the front bumper, + a couple across the top on the rack.
If you wanted rollers it'd be nothing to weld some on.