how you you find the cg point of a plane i'm building a rally nice foamy but having trouble finding the cg can any one help

Check out the internet. There are many places that will guide you in detail. Basically, the C.G. should be located at 25 - 30% of the wing cord length. Problems arise in determining the cord length when the wing is swept back or not symmetrical.

This is a cool tool for finding The CG. When you find The MAC, which means Mean Aerodynamic Chord, or average chord. Measure back on that point, 30% on an aerobatic plane. For instance, if the chord at the MAC is 6 in., then the CG would be 2 in. back from the leading edge at the MAC point.