Heck, even 10% is low for design / construction documents and construction........my fees for just design and a full set of construction documents runs anywhere from 8-15% depending on the complexity of the project and the site. Construction administration services would be on top of that 8-10%.......I can't see a contractor doing construction for 8%.

I would definitely get the details (very detailed) as to what that 8% buys you included in the contract.

Quite a few potential clients are surprised at how much time it takes to go through a project. Then of course it equals money.
I have to inform them that the plans and planning process is as important as the purchase of a furnace or trusses etc.
Thomas, it would be interesting to add a brief as to your position and location. Thanks.