Why pay 10% on top of your construction costs for an architect?
Imagine you were buying a new car, and for 10% extra you could have the car fully customised to your own personal needs, with no increase to manufacturing costs. Would you do it? The same precise analogy can be used when engaging an architect to design a home to your own personal needs and aspirations. The 10% (or whatever percent is determined necessary for the complexities of your project, be it 6% or 15%) is buying you expertise that will allow you, for the same construction cost, to create a home that has been specially customised for your needs.