Songbird Essentials Lonestar Purple Martin Goliad 4 Room Add-A-Floor with Round Door. If your Purple Martin family is growing, then this Add-a-Floor for the Goliad Purple Martin house is perfect for you. This modular aluminum addition has 4 complete, full sized rooms. Designed to fit on the bottom of your Goliad system, you can add 2-4 additions safely under your 12 room systems. Addition includes all needed hardware to mount your Add-a-Floor to your Goliad system. Door entrance holes are 2 1/8 in diameter. Each level has 4 rooms - room size is 6 inch x 12 inch x 6 inch.