The time to calmly finalize the calculations is very important. (Luckily, you can pay for the land in cash!!) I wanted to build the parking spaces next to the house (which is already there). I couldn’t detect any "slope" on my property, then the excavation contractor came to take a look. Suddenly it turned out that about 50 cm had to be retained, otherwise all rainwater would flow "backwards" into the neighbor’s garden. So much for "just quickly paving"... You still need a buffer, that cannot be emphasized enough.