We preferred to do it this way, because we knew it would be off the ground, sturdy, and with hardware included. We obviously had to improvise the roof and floor with purchased plywood, and also the hatch on the side (which we don't use by the way, I collect eggs through the main door very easily, thank you.) I can assemble things, not build them from scratch. It was also a ton of fun walking through Ikea with the mindset "ok, what can we use for our chicken coop?" My favorite find was the bottle rack...it looks like a ladder to me.
The chickens don't have a perch to roost on, their favorite place to sleep is just right on top of the nesting boxes.