Thanks! I have used SketchUp for a few larger projects, but sometimes I'm outside with the circular saw ready and realise I need to make a change, and it would be useful to be able to make reasonable sketches just with pen(cil) and paper. 

Thanks! That's useful to know, but I was asking more about the ability to draw a '3d' perspective sketch. Whenever I try to do this it just ends up looking a mess and things aren't the right relative size. 

Did you ever take a technical drawing class or anything? Or is this a thing some people can just do? 

Looks cool! I remember being excited about these when I was a kid. 

Could you share some details on how you make those drawings which aren't just cross-sections? I do some basic construction but I don't have any training in it and my drawing skills suck but I'm not sure where to start.