I occasionally build recumbent bicycles, and often clone them from a commercial model. Let me tell you how I get the measurements. I find a good profile (and other straight-on views) on the web. i print them out and find something on the drawing that I know the dimensions of (wheels are a good example). Then, I lay a good ruler on the drawing and measure the know thing. I calculate the ratio of ticks on my ruler to the known dimension to make a scale. Any other dimension can then be determined from that. It will also work for ukes. I hope that explanation isn't too confusing.