How can I do this?

I need to create a time sheet database linked to cost codes and billing –
got that covered, easy.
What he wants included is a function for progressive costing; i.e. so a
tradesman works on a floor for 6 hours and completes 25% of the floor, i need
to add something in so we can track that the floor is 25% finished @ a cost
of X (for labour) with 75% of the floor remaining and compare that to
budgets. The amount of work done will by based simply on the supervisor
estimating or running tape over it
The complication is that it won’t always be floors (square meters) it might
sometimes be digging holes (cubic meters) or some other unit of measure – he
says “just put a field in where i can nominate the unit”, I’ve tried to
explain that its not that simple, i really need a list of units to put in a
table - or do I?
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deb