What is the cheapest way to build a house?

The cheapest way to build a house is to design a simple one: rectangular footprint, standard roof form, window openings in ordinary sizes, materials every merchant carries. Complexity is what costs. Every corner you add to a floor plan adds foundations, brickwork, roof junctions and labour hours. A plain rectangle under a simple pitched roof is the cheapest enclosure per square metre there is, which is why barns look the way they do.

The second lever is phasing the finishes. Get the fabric complete and compliant, then live with basic floors and painted plasterboard while you save. Rooms can be decorated properly later (from £400 a room on our pricing), flooring can wait, the second bathroom can be plumbed but not fitted. None of that hurts the building.

Where you must never save money: structure, drainage, services and insulation. We renovate houses across South London, and a good share of our work is digging out someone's false economy from decades back. Undersized steels, bodged drainage runs, solid walls that were never insulated. Fixing fabric after the event costs several times what doing it right would have cost, because everything in front of it has to come off first. Cheap finishes are a choice you can reverse. Cheap fabric is a debt with compound interest.

Spend on what you cannot see, defer what you can, and keep the shape boring.