Additional costs
Often during the build process customers decide that while tradesmen are onsite other jobs can be done, usually this fine but will need to be costed additionally.
We often see plans change mid way through a build as customers change their mind on what they want, or change the specification of a kitchen or bathroom, add new features or change a layout, again this is usually fine but can take more time and add to the cost.
It’s also not uncommon for customers to have additional walls plastered, more sockets added, security systems fitted, patios laying or additional windows and doors fitted. Let your builder know as soon as you decide on any additions you may want included.
Timing
Consult with your builder to plan a start date. Be aware that jobs can often overrun and timescales can shift.