make sure your foundation is deep and stable. You know how the ground shifts and heaves, well be ready for that, especially around water.
My neighbor build a king post from bricks. About 150 bricks and about 6 foot high. Well, against my advice, he only built the concrete footing1 foot deep and as wide as the base. I suggested a three foot deep footing.
Well, this summer, it leaned so much do to lack of water and ground cracking that I demanded he desmantle the thing for fear it would topple over on my carport area.
Do deep, use rebar, make it wide, and mix your concrete properly.