How much should I budget for professional fees on a self build?

Build the fee budget from the appointments, not from a rule of thumb. List every professional the project will need: architect or designer, structural engineer, planning consultant if needed, building control or approved inspector, warranty provider, quantity surveyor or estimator, party wall surveyor where neighbours are affected, energy assessor, and any specialist surveys. Ask each for a written fee proposal that states the basis (fixed, staged, percentage or hourly), what it includes, what triggers each payment and what is excluded, and put those figures in the budget as their own line, with the timing, because most of them are paid before the builder starts. Percentages quoted in magazines vary so widely with the project that they are only useful as a check that nothing has been forgotten. Keep the fees outside the construction cost so that a builder's quote is compared with the construction budget alone, and keep a contingency on the fees as well as on the build, because surveys lead to more surveys. No fee figures are given here; ours are quoted on enquiry.