I think I got mine online from Home Depot.
It's actually 4x6. I thought it was 4x7. But it was fine for my 7 chickens (I have 9 now). I should also mention that 2 of those are bantam. My chickens really only use it to sleep, so I can go a little small. My climate allows for it (hot summers, mild winters). My chickens are out in the run all day long no matter the season. This brand has larger sheds, too, for around $500. I liked the ones below it, but I needed small at the time.
I added ventilation and replaced the window with hardware cloth. 2x4 along its length was fine for a roost. I had 2 nest boxes on the inside, actually. But it would have been better if I'd added them on the outside or just left them in the covered run. I also installed an auto door. This was stupid easy to cut. It's very light, so you might need to anchor it. I had it up next to the house so it was sheltered from winds.
View attachment 2490849