The house and garage are cement or cinder block.

I've used them all and think these are the best: http://www.amazon.com/Malco-FCG2-Overlap-16-Inch-T...Don't use metal flashing at the joints; it will corrode from being in contact with the cement in the siding. 

Should I get an appraisal to cement the value at this time, for future reference?

This is my Dad helping...Once we had the plywood floor base down, we then laid the cement backerboard overtop to tile.

If you do buy the building you might want to consider putting up a few more cement posts around there.

Quote from @Donny Dormady: If possible, I would stick with a nice cement floor.

Cement-based Hardie Plank or cellular PVC won't rot or be attacked by the bugs.

It is a pier and beam house with two supports on a cement porch and the third post is on a leaning pored cement block approximately 12”x12”.

Make a test "wall" with some spare tile and wallboard or cement board first, and practice on that.

You need strips of cardboard or dowels as spacers, contact cement and a router.