Drawings form part of the agreement
A short description such as 'build rear extension' leaves too much open to interpretation. The contract should identify the drawings, structural information and specification being priced.
Variations need a process
A client-requested change and unforeseen work are not the same thing, but both can affect price and time. Record them before the work disappears behind finishes.
Programme and access need realistic wording
Weather, inspections and specialist deliveries can affect dates. The contract should still state expected start, sequence and completion arrangements rather than leaving the programme entirely open-ended.