Talk:Building Your Town/@comment-67.232.144.51-20120818091908/@comment-220.255.2.136-20121001041218

If by cement upgrade you meant the cement walls of the perimeter, then yes there's one further upgrade in which you get fortified metal gates for your supply depots.

After that I've not seen any new upgrades and I'm at 28 depots now. I can't recall when that upgrade was but maybe close to the 20th I reckon.