The solution is 1.

1 floor filled with 1x1 rooms, all at level 1, with 1 elevator at 1 end.

Make sure the elevator is placed before all your rooms, that way once the deathclaws reach the end they must backtrack and attack each room a second time to reach the lower level.

Fill each room with your best dwellers and a Mr Handy if you can.

Watch as the deathclaws drop 1 by 1, then sit back and enjoy a cold 1.