Set the bill of quantities once, then raise R.A. bills against it as the work gets done.
On a unit-rate contract the argument is always "how much of this item is actually done?" A bill of quantities you can bill against — line by line, bill after bill — settles it.
TameerBook holds the BOQ for a project and lets you raise running-account bills against it, carrying quantities forward so each bill picks up where the last one left off.