I am using a 2D top view sketch to model a house. The sketch is a very rough top view drawing with some handwritten notes (no side, front or back views). The top view of the roof rafters have brought me to a halt. The 2D measurement is 20 ft. The pitch of the roof (simple shed) is 2:12 (9.462 degrees). My first thought was to use simple trig, but now I’m not so sure. Seems the base of the right triangle is 20 ft. and knowing the angle I can calculate the hypotenuse. It seems logical that the hypotenuse would represent the actual length of the top truss. But with a top view, am I looking at the hypotenuse or the base (leaning toward hypotenuse)? Can’t seem to get my head around looking at a top down view of an angled piece of geometry. Tried some simple drawings, see below. I now see the importance of a complete set of 2D drawings. Also see why a simple 3D drawing can convey much more information than a whole set of 2D drawings (also to a much wider audience).

In general when converting 2D drawings, is there an effective workflow that generates more accurate 3D representations, given incomplete/inconsistent 2D drawings?

Any help is greatly appreciated.