Meet Leonard! He's a level and he wants to help with your project. Just give him a tooth, don't tell him how creepy his smile is and you've made a new friend.

This bubble level replacement uses a marble or ball bearing instead of a liquid filled capsule and can measure angles up to 15° in either direction. I designed this to fit some marbles I found around the house that are nominally 14mm in diameter. Without having to scale the model, it will fit marbles or balls between 10mm and 16mm. The opening is 10mm wide so anything small will need to be scaled down to prevent escape. Anything bigger than 16mm should be scaled up to avoid contact with the print head. 

Pause the print at the height of the ball (in my case 14mm). Insert the ball into the slot and resume the print. 

I experimented with incorporating a print-in-place ball or pin, but that didn't give smoothe enough motion to rival a bubble level's precision.