This is probably the simplest part of this project. Since my greenhouse was only 4' X 8' the walls were pretty easy to handle. It's always best to have someone help you with this. Once again I don't have pictures of the project in process but will try to point out what I'm talking about with doctored pictures.
Just start with one wall and nail it into your foundation. Now add the adjoining wall and nail it to the foundation. Before you nail these walls together make sure they are plumb in all directions.
Repeat this process on the remaining walls.