When you have a flat, treeless, rock-free lot, with good, compacted soil and a sewer system already in place; the site preparation cost might be zero.
Flat, fairly leveled lots are cheaper to build on than sloping lots (mountainside).
The most expensive scenario of all is the sloped, wooded, rocky lot that usually requires an engineered foundation.
Maybe your house need to be higher than the road, or need excavation, backfilling, compaction, a retaining-wall, dewatering and/or runoff control measures etc.
Different soils have different load-bearing capacities. Don’t start your foundation until a compaction test gives you a positive result.
Oh, and make sure you OWN the lot; you wouldn't like to build a house on it to find out later there are some legal problems. Check for encumbrances, is the lot maybe used as collateral for a loan, do you have 'right of way'.
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