Mostly you can tell by the fact that plants that are considered reliably hardy in your zone, & grown by many people here on the forum in your zone, DIE in your garden over the winter, either never returning in the spring, OR by trying to return in the spring by sending out one sickly sprig & then quickly dying off, & they do these things for you over multiple attempts at growing them. Believe me I have plenty of experience with this. Why this happens is somewhat a matter for speculation. My experience has been that plants labelled with cautions about drainage (beyond the "moist but well-drained" nonsense that is on so many labels) may have considerable difficulty overwintering in my garden, despite zone compatibility. In addition, plants labelled for zone 6, which some people around here can grow, will almost NEVER survive winter for me, unless planted under the eaves at the highest point in the yard. Zone stretching is painful here. I blame this on "winter wet". My definition is somewhat broader, however, than Whaas's is. I can have this problem just about anywhere in my yard. I garden on very heavy compacted clay - where everything drains slowly. I have gardened on this clay (I still don't call it soil) for over 15 years now, constantly amending & improving it, with some gains, but a lot of plant losses. In very cold, consistently cold weather, with good snow cover, my losses are now usually slight. In a year with freezes, ice storms, occasional snow cover, odd warm spells, followed by winter as usual, losses are high. My theory is that many of these plants survive my winters, just not my sometimes nasty autumns & wicked springs. To combat winter losses I use every trick in the book. Amending soil & planting under the eaves I have already mentioned, & raising beds is certainly helpful, along with selecting plants that are moisture loving (remember most of these still need some air in the soil), always picking major shrubs and trees compatible with clay, & planting high, using mounding & little shelves, etc. I find that rock works the best, big rocks, little rocks, gravel & grit & granite fines, in the soil and on top of the soil. Commercial products like Profile (fired ceramic bits) can do wonders but are expensive. We could not keep a front curb tree alive in our (very non-urban) setting (probably because of the piled snow Whaas mentioned, rather than the dry heat so often associated with these locations) before we discovered it. A mailbox planting is out of the question, I'd have to raise the mailbox too high for the mailman. :))

All you need to do it make sure that there is decent topsoil in the planting space. The stone and sand will be unnecessary, since where would the water go after the air spaces between stone and sand is filled up? Don't create those air spaces to begin with. When you bring the level up to the concrete slab and plant it, drainage will not be a problem.

well an update for anyone that cares, we hired an engineer and he said the bid that only had 13 piers was "a joke". seller wouldn't pay for the other bid so we terminated the contract.

Thanks again @res2architect. Thanks to you I have someone who is going to apply the Tuff n Dri after we pour the walls. Now the question I'm wrestling with is the exterior drain. It's going to be around $5K with the plastics, gravel, pit for the water to drain, etc. We're backfilling with septic sand so some people think I can get away with that but I'm hoping to have this house in the family forever. The guy doing the foundation said he would do it "if he had the money" Curious to get your thoughts and thanks for the rec on the insulation, too.