A typical self-build runs through site acquisition, design and planning permission, detailed design and building regulations compliance, tender and contractor appointment, construction with stage inspections, and completion with certification and connections.
Each stage has a gate that should be closed before the next begins. Buying a site before checking planning feasibility, or starting on site before the commencement notice is validated, are the two most expensive sequencing mistakes.
On a typical one-off house, design and planning take six to twelve months, procurement one to two months, and construction ten to eighteen months depending on scale and method.