Possible odd question.

A while ago I wanted to setup a pond outside, but after playing with reef
setups and salt water I am thinking of the idea of making an outside salt
water tank, but not the usualy glass type, I was thinking of making a wooden
frame about 3 meters x 3 meters and about 1 meter high then sealing it with
fiberglass, then adding in the usual pumps and filtration and putting in
some live rock and some fish. It's be able to save heaps on lighting the
setup and put that money into maintaining the temprature with a decent
chiller.

I would like to hear some feedback from people about this idea and some
possible problems I might be looking at. Or some possible good things ?

I was thinking that it might help in growing some alge on some new rocks
fast then in a normal tank too. ??