I don't use bracket kits. There isn't that much framing in the roof of a typical chicken coop (avoid the barn-style "gambrel" roof designs, waste of materials, doesn't provide useful space) because the typical chicken coop just isn't that big. With rafters placed 2' on center, you can carefully walk on the roof for installation and repairs, yet you need only 5 boards (and only five functional cuts - the other 5 are for appearance) per side for a gable roof, and technically none if you do a shed roof.
You may find it easier (and relatively cheap) to make good strong roof ridge joints with
these. I use them in every build.
DO recommend either 8x6, or better, 8x8 - reduce cuts, adds little to your materials costs, but substantially increases available space inside.
/edit prices being what they are right now, I recommend a metal roof for economy and ease/speed of build. Spend the couple extra $ per panel, get a "5v" design, not the wavy things, not only is the gauge of steel thicker typically, which is good for durability, but the broad flat areas make attachment easier, more secure, and less prone to leakage in the long term from thermal expansion/contraction. DO USE GOOD GLOVES though, that metal is SHARP! [safety third!] Disadvantage to a metal roof is cutting. Can be done, but I try to avoid it. It would be easiest if you did a single sloped "shed" roof to avoid cuts, and place most of your all season ventilation directly under the overhangs.