which version of UG are you using??
As wheelguy posted,first boolean substract would be perfect,,or other options would be as follows
1)trim body(u can trim the body as u need using planes..)
2)divide face(u can do the same using planes,surface,wcs etc)
Is your problem is how to create a inclined plane?if so,provide some details it would be easy..and anyone of help you,i think to create inclined plane you can search previous posts
UG NX5,SOLID WORKS