Build less and worse per unit. Share foundations, roofs, walls, and common areas. Build less square footage per unit. Build less fancy per square foot (cheaper kitchens and baths). Use all standard materials and finishes. Install low-end appliances and HVAC. Everything cookie-cutter; no per-unit changes. Use less land per unit (and maybe less expensive land overall). Have no private outdoor space (or just a tiny balcony).

That’s not well aligned to how to maximize profits from a given unit though (fairly obviously and by intentional design).