If i may throw my 2 cents in here... They work great. However as has been stated before: Need ventilation. If i may make a suggestion it would be, keep them off the ground. The bottom rusts out quick and when you level the container, don't make it level. The water will "pond" on the roof and that creates problems. A slight slope on the foundation is all it takes (1" in 10'). The roofing material we used was some kind of silver/tar cold patch. Works great but buy a new pair of shoes when you're done.

when I had a flat rood we used something similar to this https://www.homedepot.com/p/Henry-4...TUcV9IoIWUaAn0NEALw_wcB&gclsrc=aw.ds

every few years we climbed up on the roof and spread the tar with aluminum in it , very much like sealing a drive way

get it clean and dry and spread it around with a broom/tar brush

my parents neighbor was putting a garage on in about 79 he got the pad and and walls framed but was running out of time and money , he had wanted to do an attic over it for storage so he was laying floor joists and a deck any way he put a little pitch like 3 inches inches over 25 feet laid the deck and put 3 layers of 30# felt on it and some drive way sealer it worked , he got busy , so he found about an hour to sweep and brush on a coat of drive way sealer each year , he was a road crew foreman if the weather was passable for the next 20 years he was hardly home. 40 years later that flat rood hasn't leaked and has never been replaced drive way sealer is still cheap but his roof did cook being black the underside was warm in the summer it was attached to the house by a breeze way so it didn't cook the house so they lived with it.