I draw things the old fashioned way, using old school drafting techniques. Nothing special here. Just a pencil, ruler, some drafting triangles, a compass, protractor, ect. I'm working on drafting up some plans for a trailer I want to scratch build right now, in fact. I'm drawing the plan out full sized, in 1/15th scale, but I am scaling all my dimensions off of a print I found on the internet. If you know some really basic math, you can solve for any unknown dimension, measured on a print, as long as you have a couple known reference dimensions provided. I just figure out what I call a 'scale multipler' and then go from there. Anything I measure off the print, with a ruler, can then be calculated to solve for any unknow 1:1 dimension.
Here's a photo to give you an idea of how I do things. It's a CAD drawing, actually. That's cardboard aided design.
The trailer is 42.375" long. I didn't have any paper long enough, so I found some cardboard instead!
I know it's not the greatest photo ever, but my drawing of the trailer in 1/15th scale was hard for the camera to pick up. You can see my tools and the print I was working off of in this photo.