I built 2 houses in the last 2.5 years, and have run the numbers on just what you are talking about. there are a few variables and considerations. like Lot limitations like what will fit, and what will the municipality allow, Drainage plans often dictate where your building envelope has to be on a lot. Also foundation type, the less excavating the less cost. Its always cheaper to go up than out, Lumber is still a lot cheaper than site work and concrete work. Corners are Expensive, the cheapest is a square or rectangle, every outside or inside corner on the exterior complicates foundation, roof systems adds cost to siding, sofit and fascia, gutters, as well as interior, like drywall, trim, ect. if you self GC you will spend $150/sq ft at minimum with lumber in flux as well as labor being difficult right now. $175-200/sq ft is probably more reasonable. also consider 3+ family in the new construction world is commercial for fire protection code and will require a sprinkler system, this can be worked around in some municipalities with fire separation walls essentially joining 2 duplexes together, but that depends on local code enforcement.
Design and finishes can translate to better rents, basic is not always the best, not is high end, you need to determine the sweet spot.
New construction is definitely a long game, with narrow margins, consider what rents may look like especially in a tiny community, they may not support even 1% But if you have a Pile of cash to park it may not be a bad way to go.