I'm working on my deck design, and sometimes I feel like I get lucky when doing extruded cuts, meaning I am clicking what I think should be clicked and the cut works out for me, haha.  I am doing these in the assembly, as not to change all the parts in my configuration.  If you look at my picture, I managed to cut the studs parallel to the rafter without issue, but obviously the studs and rafter are still taking up the same space, so I have to cut that out.  I have a hard time telling what plane to start the sketch in, which entities to convert, when to convert entities, when not to, etc.