Have you thought about a pre-cut package coop? In the States there's quite a huge selection to choose from, and I think many of them come with decent instructions, you can probably find reviews on them on this site. That might be a good direction to go, if you don't know which end of a hammer to hold.
Another idea might be to find plans for a shed and just modify them a bit to suit your needs.
That being said, most building projects have a stage where you've screwed up something and need to make changes on the fly. Usually if you just make a simple plan and start building, you'll learn as you go and end up with maybe not the prettiest result, but the sense of pride you get from looking at something you've designed and put together yourself makes up for a lot of flaws.
Also, even with great instructions, the site where you build will be individual, so you'll need to make a foundation that suits the spot. Once you've made a level foundation, it's pretty easy to put up a frame, and after that it's only cladding and detailing.
Believe in your ability to create something and learn new things, and you'll soon have a chicken coop in your own back yard!
