any 1 know how to build wood kicker ramps for a crf50

 

same way you build one for anything else.

check out the numerous ramp plan sites, but add a couple more ribs on the transition to make sure it'll take the weight of the fiddy (and you, if you're fat)
seriously though, most plans you find for skateboards and whatnot will work just fine with a little extra support. and either wedge the back of it against a curb, or lay a couple strips of rubber along the bottom, so it doesn't slide when you hit it. best of luck to ya. back flips are in your near future.

 

and throw a 12 bar on that fiddy