Underbudgeting contingency

Ten percent is a starting point. Fifteen is realistic. Twenty is wise on older properties. Do not pretend the contingency is profit.

Verbal agreements

Anything not in writing did not happen. Variations, programme changes, materials substitutions — all in writing, signed by both parties.

Skipping the paperwork at handover

Trade certificates, completion certificate, manuals, warranties. Chase them all before final payment, not after.