I need to find out about how the suppliers work where the house will be built. I now live about 300 miles to the south so I don't know the area well, except for the geography.
When I built the cabin my main lumber supplier used trucks with tilt beds. They basically tilted the bed until the lumber slid off the back of the truck with a big crash

After dealing with the resulting messy lumber piles and some split/mangled lumber at the bottom of the stacks I swore I'd never have lumber delivered that way again. So after the heavy duty foundation lumber and 2x6 framing lumber was delivered, I switched to suppliers that would come with a piggy back fork lift

Deliveries got a lot less stressful. And I didn't have to haul the materials from the edge of the drive to the backside of the cabin by hand anymore.
BTW The deck on the front of the cabin is 36x6' and 4 ft off the ground. Once this was in place we used it as a long loading dock that allowed us to hand unload long lumber etc. (e.g. the 4-24' & 4-36' long Doug fir GLULAMs and 2x8x20' long rafters) off the SIDE of lumber trucks. The decks of lumber trucks are about 4' off the ground; so the deck and the truck bed were about level.
You really need to think through exactly what you plan on unloading using a loading dock. For example, how big, how heavy and what shape will the stuff be? And more importantly, will your stuff be on the truck where it can be reached from your loading dock? And easily moved into your garage.
So far I guess no one likes the idea of a portable loading dock with a ramp for a forklift. Seems like the most flexible solution to me.
The building materials that you'll be unloading are likely to be very heavy (measured in tons per bundle/pallet, etc). So any portable loading dock would have to very stout to handle just the weight of the building materials, let alone the fork lift. etc. For example I just got a delivery of 60 - 80# bags of concrete on two pallets. 40 of them were on one pallet and 20 on the other. 40x80 => 3,200lbs/2,000lbs => 1.6 tons It takes a pretty heavy tractor / bobcat to lift 1.6 tons (without tipping over). The delivery truck used the piggy back to put them down right where i wanted them.
FWIW the standard delivery charge w/ piggy back is $35 from a lumber yard about 30 miles from here. The highest I've paid is $50 from a yard about twice as far away. The cost with out the piggy back is the same.
Funf Dreisig