My recommendation would be to use some kind of angle protractor/square and bevel like in art school or math class and just go manually. Check out the video. 

Maybe there is an APP in the Miro APP directory i am missing. 

Good luck @Lewis !

This is totally cool!

One suggestion: I have my own private “support board” just to store icons, images, shapes, and things that I very frequently re-use. So that instead of re-creating the wheel, I can just “dip into my private stock” and pull up something quick.

I will definitely set up some predefined angles like this and store them in my support board!