Our family has been building pallet structures for maybe 15 years.
We've sold one which was wired for being a repair shop for electronics and
small tools -- work benches with lots of outlets for power and good
lighting overhead.
Right now, we have one which holds junk and our second freezer.
Another is a playbuilding for a child.
We used scrap metal from leftovers a friend of ours has on metal building
construction sites for the roof.
Old windows and doors.
Another pallet with plywood on top for a deck/porch.
Our finished buildings look a lot classier than the one in the web site.
We have one which hasn't been finished on the exterior and looks like a
wood shed.
We put all these buildings on concrete block and they are constructed so
that they can be lifted to a trailer and taken away.
As long as they are mobile and not over a size, the tax situation is
different.