Project's material usage

Hello all!

I am might missing something, but the way the system seems to work is you set proposals for a project, you than have orders and you make orders.

Which is fine if you are buying the exact amounts from your suppliers.

Howevere realistically, I qoute a job for XXXX EURs, than make some purchases so we can actually complete the projects. I assing these purchase orders to the project and I get margin at the end which is not even close to be true.

The reason behind this is we build a house for example, I give an estimate, the buyer likes it, he/she makes an order. At this point I know I am going to be paid this ammount. However I buy stuff in boxes, truckloads. I still have stuff remaining on stock after I finished the project, sometimes it can be thousands of EURs depending on what was left in the warehouse.

Is there a way to make a stock movement for the project so my stock gets reduced, and I can see the actual money spent on a project? What settings should I change?
Is there any 3rd party module that does this?

Thanks!