Reply by yrob

You will have to joint the boards. 2×4s come with a rounded edge and are not ready to glue. You can do that pretty easily with a jointer plane. Once you have a good edge, you can glue them together in groups of 3 or 4. Once its dry, you again use your hand plane jointer to flatten the surface. You repeat for 2 or 3 groups and then glue these together and do a final planing.

-- Yves