I am new here...been lurking a while and love this forum. I am a carpenter by trade and something you need to consider is what kind of pine you have: It comes in two varieties....yellow and white. The yellow tends to be highly resinous and resists rot better than white pine varieties. In the early days, it was used for masts on ships, log homes, and railroad ties. Certain varieties of yellow pine are considered pretty much a hardwood and are the main wood used for walk planks on scaffolding in our area.
This link tells a bit about it:
http://www.thewoodbox.com/data/wood/longleaf-pine.htm Their are also other varieties of wood that are very resistant to rot and termites (another MAJOR issue)...most of the slowest growing hardwoods are very dense and hold up very well. Up north the best I've heard of is osage orange. Due to it's size though, those are only large
enough for smaller projects like fence posts etc, but are reputed to last forever. Where I live now, my bets are on live oak...it will barely even burn.
Either way you go, keeping the wood out of the ground may be your best option. We are preparing to buy our own lumber mill and starting clearing some of the trees off the densely wooded portions of our property: We need pasture and for that the ground needs some sun. We have a lot of lobolly (Southern yellow) pine, gum, and oak here. We are adding a timber frame porch/entry area and we are looking at pouring support piers and attaching the posts above ground via hardware since we hit water when digging holes for fencing here. We plan on encasing that in stone pillars up to three feet with a tapered top cap to encourage runoff. Add eaves that are over 18" and guttered and you mitigate the water damage to minimum.
Now, this is just for porch areas...your main structural lumber will create other difficulties for you: Anything you do that creates an opportunity for water to get between two surfaces (pier and post bottom) will be a place for rot to set in. If you build off the ground you would have to
shelter the connections from getting direct rain or retaining too much humidity. It is all very complicated, but not impossible.
To encourage longevity in wood exposed to the elements, you are also going to have to coat it with some sort of protection periodically: Raw wood will be dried, warped and damaged by intense sun and rot with time no matter what you do....water finds a way in and always wins.
We live in a VERY hot wet climate....SE Louisiana and our house has Cypress siding (here when we purchased it 3 years ago), so we must seal it; or between the sun and rain will end up replacing it in a couple years. The process is time consuming because I prefer to brush it on since it penetrates the wood better than spraying. Rather than use the nasty epoxy that is recommended we use a semi-transparent stain or you could use thompson's water seal. I'm not sure if theirs any natural way to seal the wood that will last, it may be worth checking into.
Also, no matter what sort of building you decide to undertake....make sure to shoot grade with a transom or builders level prior to beginning if possible. If you can build on higher ground or bring in fill to create higher ground that will aid you as well: Having proper run-off will make sure you don't end up building in the middle of an area that holds water. Even if you are on a hill...it is still worth double checking. If you can't access the transom, just go to the site after substantial rain events and note areas that puddle and hold water...see if you can figure out where the water goes and make sure not to disturb that or build in its path. We know a gentleman who built in an area where no permitting is needed. He put up a very nice home up the hill from a large lake. The only problem is that the first winter after he built, the area experienced torrential rains. Not only did the lake flood up to his front steps, but all the runoff from the hill behind him ran right under his raised home. He ended up doing extensive trenching to stop the river from running under his place. Had he not been on piers, he would have had a disaster.
Just my two cents; I wish you the best of luck with your project and hope you post your progress so we can see how you do!