I have several 20's lined up. They are about 12' apart from each other and I spanned the gap with corrugated sheet metal to make carports and work areas. I even find with 20' that it becomes hard to get to the back. Storage in the rear gets damp, and sometimes rusts. It is dark even 20' back. I would buy two 20's before I would do a 40' even though more money. It is also easier to move a 20' with a truck and roll it around on pipe. I have had both 20's and 40's, and the re-sale is better on a 20'.