First off, I got the greenhouse when it was on sale so that was already a plus. My brother and my husband helped me build it. First thing when unpacking all of the pieces we noticed the great quality. Building it was definitely a project but the instructions were pretty straightforward.  Took us a few days but it was also in the dead of summer and was 100 degrees out! It turned out fantastic. All the pieces lined up wonderfully as well as all the pre drilled holes!  The only thing we had an issue with was the metal flashing pieces were quite hard to install. Other than that it was great! 
I couldn't be happier with it except I wish I had gotten a bigger one! 
I think the only stuff I had to buy extra was gravel for the floor and 4x4's for a base.