I have a simi poor draining soil and some low spots that holds an inch of water after a rain. Would a mound 3x3 feet thats 6 inche's high be good enough to plant a fig tree?

Hello and welcome zorkan.  I also have a high water table and was advised to elevate the surface 50cm or about 20 inches.  It seems to have worked well in my first summer and kept my first fig tree in a big open-bottom pot I had buried to ground level from dying after raising it up. 

Welcome Zorkan. I live in Southern California and my soil is poor draining clay. During the winter, there is also an half inch to inch of water building up around the tree for a short period of time. However, I believe your area gets a lot more rain than my area. The rest of the year in my area is very dry. So from my experience, standing water does not bother figs while they're dormant. However, standing water does negatively affect fig trees while they're "awake". IMO, a mound would be a good idea.

Hope this helps! Best of luck!

You will need more than 36" square to accomodate the roots of a decent sized tree. Roots can spread as far as  from the tree, maybe more.

Hi Zorkan,
3'*3' is ok, but 6" of height not IMO . 2' of height should do it .You could use a big plastic pot with bottom removed to make that height .