My husband spent about $600 building a
loft in the
garage. He used half of our 2-car garage. Built a raised plywood floor. Built the inside wall about 6 feet out from the rear of the garage. Divided into three sections. The ceilings are wire mesh a couple of feet lower than the inside ceiling. A main area, an area for YBs and a breeder section. He cut holes in the outside wall for 2 Belgian trap doors, and 2 sections, probably 6 inch by a foot ventilation areas at floor height. There are outside aviaries for the 2 main sections. I don't technically have a landing board, but the outside aviary sections have a kind of slanted roof (out of wire mesh) with hinged doors that drop open so the birds have easy landing access.
The aviaries are south-facing and we get good sunlight and ventilation. Seems to work well for me. We live in town and didn't have room for a nice-sized free-standing loft.