User395221
Crowing
You can also just putty it up and redrill, use a bigger sized screw if the hole is enlarged, or just move the screws. Or you could use other ways of fixing the sides (hinge them, use channels to slide them in, hold them on with swivels).Depending on what kind of screws are used, how carefully clearance and pilot holes are sized and drilled, they can be reused quite effectively.
I'm not keen on A-frames either, for the reason aart said, the space at the apex isn't that useable, but it's up to you. (I have a sort of "pet claustrophobia", I get uncomfortable if my pets don't have plenty of room - not sure they care, but it bothers me.) I'd prefer a "box" shape.
How are you thinking of supporting the floor? Where would bolts go? For the "slide-in" option, that might be ok immediately after you've made it, but after it's been out in the weather and pooed on by chooks the timber will change, it won't stay exactly the same size as it was, it might warp a bit and getting it out and back in might be a challenge. You could cut it a bit short on either side so you could be sure to get it in, but that would give you crevices for poo to get into....