Aaron Ronas

Putting it simply, is it against the rules to build and KEEP a building or creation upon abandoned land AFTER it was abandoned? IE: Land is abandoned, man comes along as permissions are still laid upon the land. Moves a house in, etc etc. IE: Land is abandoned, man comes SITTING on a house because permissions are NOT set, and leaves it there. Most abandoned land I have seen does not have a return timer, does this mean they allow it? Or does it infringe upon their held land?