Soft costs are the pre-construction and non-physical spending, and the ranges below swing hard by jurisdiction, so treat them as orders of magnitude rather than quotes.
A stock or lightly modified plan set for a straightforward single family home tends to run in the low thousands, maybe 3k to 8k, while a custom architect-drawn set on an odd lot can be 15k or more. A boundary and topographic survey is often 1k to 3k. A geotechnical soils report, which your engineer will want and your building department may require, is commonly 1.5k to 4k. Civil engineering for grading and drainage varies with how complicated the site is.
The two that surprise people are the ones you already named. Impact fees, which cities charge to fund schools, roads and utility capacity, range from almost nothing in some places to 40k or more per unit in parts of the west. Tap or connection fees for water and sewer are separate from impact fees and can be another five figures. Call the building department and ask for their current fee schedule in writing before you remove your contract contingency, because these are published numbers and there is no reason to guess.
The cost you can't invoice is time. Plan review and permitting can take weeks or many months depending on the jurisdiction, and you're carrying the lot the whole time. Construction lenders generally fund from the point you have permits, so the plans, studies and fees usually come out of your own cash. Add up that number honestly, because it's the real minimum you need liquid before you're a builder rather than a lot owner.
