Beginner Little Crab

Here's for finding angles with a framing square...

http://www.shopnotes.com/files/issues/114/framing-square.pdf

 

SamSam posted while I was sorting out my scanner.
Same principle used.
See attachment to draw 78 degree angle, vertical 10 inches high
horizontal 2.126 inches wide which is almost exactly 2 1/8 inches.

 

Roof pitch calculator, good for all angles not just roofs.

http://www.pole-barn.info/roof-pitch.html

 

Yobarnacle, Thanx, but I think this calculator is the most correct and universal http://myrooff.com/roof-pitch-calculator/

 

First of all good for you that you're involving your young son in this project.

I don't know how much money you're planning on spending. That said I have found that a rotary laser level has been quite valuable in boat building as well as decks/sheds and all sorts of interior design work. Not only can you get a jig or any structure perfectly level, you can also "paint" a perfectly straight line between any two points (or extend a line) regardless of orientation.

Something like this in case you're not familiar. You can spend more or less depending on what features and quality you desire.

http://www.amazon.com/Johnson-Level...1442173440&sr=1-9&keywords=rotary laser level

Good luck, go slow and remember boat building is supposed to be fun.