Finished the roof this morning. The gable isn't a great fit, but the flaws are under the soffit... so, "F" it.
I put the coin battery into the underside of the carved pink foam base. For the moment, this works pretty well -- the foam presses the wires from the LED into the battery nicely. In the long term, I'll be able to pull the leads down and work them into layout wiring.
Next: painting and landscaping the pink foam.