Receipts for labour
Well the receipts for labour would be taken into account.
But say, in theory, that you were actually building yourself, then we use an industry standard to calculate the stage payments. That is to say a price for work done, per square metre, at different stages of construction.
Remember, it's our job to be appraised of how much it costs to do x, y, and z so the engineer should have a fairly good idea.
Just a word of warning though, at the moment, we have a policy of not touching self builds with a barge pole. Self builds require much more supervision and hand holding on our side and can create problems in relation to insurance for us.
If you can afford it, I would recommend employing a reputable builder with good insurances, they're worth their weight in gold.
HTH
Mo