couple of things:
1" higher on one wall isn't giving you enough fall to get good run off when it rains. You don't say where you live, but if you get any snow at all, when it melts it's not going to run off fast enough.
How wide is your coop going to be? because 2x4's won't hold a lot of weight even standing on edge, you didn't say how far apart you spaced them, but closer is better. Although even better would be to go with 2x6's or 2x8's. There are plenty of online videos available to watch on how to build a shed.
If you have a metal roofing dealer close by, you can get your metal panels from them cheaper than you can from the big box store, and they'll cut to the length you need.
Also another thing, if you're getting your materials from a big box store, IE: Home Depot or Lowes, they'll cut plywood or lumber to your dimensions if you need them to. When I built my coop, (see my build here:
https://www.backyardchickens.com/t/955919/future-coop-and-run)
I had them cut all my siding sheets to length for me, I only had to cut out the doors and windows, and a couple of rips long ways. I mostly just put them in place and nailed them up.