If you're gonna build a tower make sure it's safe...
Use 4x4's in the corners... And make sure you burry them atleast 6' into the ground... dig the holes about 7' and fill the first foot with rocks and crushed limestone and then drop in your 4x4's and fill the holes with concrete...
That'll give you a sturdy base to start with... when you add the floor to the tower make sure you use some good solid 1/2 inch bolts and washers to support the floor joists to the 4x4's and then covers them with plywood...
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