How do I build a bouldering / climbing wall?

I want to build on the inside brick wall of my garage, to finish up with an overhanging wall. The problem is that I live in England and we don't have much space - I want the wall to fold away but don't want to use ropes or chains to get the overhang as they'll allow the wall to sway as I climb. Pivoting at the bottom of the wall is simple using clevis and cotter pins, but how to fix the top is problematic. If I use 2x4s bolted to the brick wall and 2x4s on the ply, they're adjacent - I then can't fit another piece in to hold the wall at an overhang angle. Any advice / suggestions please?