If the work relating to a variation is going to extend the length of the project, make sure you also provide the home owner with a written notice of an extension of time (your written contract with the home owner will specify the exact steps you need to take here).

Finally, make sure before you sign contracts with the home owner, that your building contract allows you to refuse a request from the home owner for a variation.  This is because there may be times when you simply do not wish to carry out that additional building works (i.e if it will significantly extend the contract period and you must start another project immediately after you are to finish this one).

The above tips, if followed, should significantly reduce the chances of a dispute arising as a result of a variation to the building contract.