Think of it this way.....If you want quality then you cannot compromise on the steps. Nothing worth anything comes quickly. Sure you can buy a coop, spend a ton of money and that will be fine - but the builder hopefully, if it is a quality coop, spent time on that coop and didn't just bang it together. But then the price is high because you are not just paying for materials but the builders time as well.
Set yourself a goal. So many hours each day or an hour each day - give up a favorite TV show and spend the time building the coop. If you disapline yourself to do it, the job will get done in good order.
Sometimes building fast and taking short cuts means problems later. And sometimes someone is a skilled builder and has worked out the system of building so the job goes more quickly. My second coop went up way faster than my first. I also took a few liberties and made some mistakes because I was cocky. My first coop was better built because I followed the directions carefully measured twice cut once and then cut again - got another piece of lumber had to cut it again.....It was my first time building anything from plans.....
My third coop was built from Pallets - everything was Free including the nails. Added some paint - It was spiffier than the other coops!
Don't beat yourself up
All in good order
Caroline