I have been considering building this passive solar greenhouse. It is 12' X 24' It is 12’ wide and two rows of grow beds and the 55 gal barrels would leave about a 2 ½ foot walk way. I would like a little more room but I think this would work.
Passive Solar Greenhouse | Bradford Research Center
There are a couple builds of it on here.
http://www.builditsolar.com/Projects...htm#Greenhouse