I got home from work and rushed to print and cut the roof and truss pieces I designed last night. They worked perfectly!
Here's a shot of the slot and tab I used this time. It holds in place very well on the truss, though it might feel a little clumsy setting it up.
Here's a lousy shot of the slots on the truss:
I'd like to try the same setup, but rather than a slot and tab, I'll try one or two tabs, and see if it still holds in place well.