I think I would shim the bottom with wedges to the angle (lean?) you want. Maybe even hot melt glue so nothing shifts. Then use a scribe block and pencil like when scribing a line around a chair leg and scribe the bottom line, then rig up another scribe block for the second, and another for the third. The higher up, the more stable they (the blocks) have to be. Cutting? I think a good old fashioned cross cut hand saw... Please post pics, I love your work and ideas...