You can certain put a house on a crawlspace and have it be accessible. I do not know how much of a "ramp" is needed to go that far above grade, however my old house was built over a full basement and the driveway and back patio were both at entry grade level.

The garage was on the north side of our house, and the driveway rose up to the 1st floor house level on that side. The driveway was paved all the way along side the house. You drove up the drive into the garage, and could enter the front door just a few paces away -- all without steps into the house. You could also pass from the garage into the house without any steps. The yard on the north side of the house was a couple of feet higher than the south side.

Our back patio exited out the west side. The patio exit at ground level-- no steps from the house out to it. On the left side (south edge) of the patio there were 3 steps down to ground level. All the basement windows were on that side(south side) for egress purposes.

Depending on your lot and the overall footprint of your house, in the overall scheme of things, grading is cheap. You'll be stripping topsoil off the site anyway, so moving some dirt on site and even adding some retaining walls if you have to, would seem like the way to go to get a slab on grade and have the entire first floor accessible.

What is the slope of your lot / elevation change you are dealing with? How much land? Footprint of house, etc. If you have enough space, you can grade everything flat and taper into the existing topography without retaining walls at all...

I cut 5' and filled 10' and surrounded my building site with retaining walls in order to put a nice flat building area in the middle of my treed acreage - but I did that because I wanted to keep the area minimally disturbed and not lose specific trees. If I could have stretched the disturbed area / eased the slopes, it would have been a ton cheaper to get to my flat space.

loonlake - that sounds like what we need! I would like to be able to get to yard from at least one side of the patio without a step. So, not being technical, it sounds like the basement was under the house up to the patio and then the part of house from patio to entrance to garage was on a slab. I guess we would need an engineer to design that. We're trying to avoid retaining walls, I remember our current one was expensive!
The builders I've talked to are discouraging cut and fill as very expensive, but I imagine the test is getting estimates with both types of foundations.

thank you!