Oh Luc, it's full already. I may need to install some double decker shelving as I did in the Little Greenhouse, see picci. Trouble is, I would probably knock my head every time I want to reach what's underneath.
Looking at the picture reminds me of the early days when it was full of vegetation. I was cutting it down and reaching forward to get hold of a wayward branch when my foot didn't find solid ground and instead I stepped straight into a very deep water tank that I didn't know existed. Well, it was January - no more work was done that day. My right leg was pretty frozen by the time I got home. How we laughed .....
I later found out that each greenhouse has a galvanised water tank hidden under a bench, 1m x 1m x 1m deep, all interconnected. What a good idea. But one of them leaks, so all leak. Oh well, can't have it all!