A custom home building project is very difficult to plan. There would be no choices or features which would be predefined in case of a custom home. You build a custom home on a plot of land that you already own. But, there may be cases where you would consult a builder before buying the land. But, the ultimate decision will be yours.
If you already have a floor plan for your new custom home, you can submit that to the builder and he will construct the new home based on the plan. If you do not already have a floor plan, you can hire an architect to create a floor plan from scratch. You can ask the builder as well for inputs while creating the floor plan.
Most of the times, the builder would be different from the architect. But, in some rare cases, the builder would double up as the architect as well. But, it is quite uncommon and in fact it is recommended that you hire an architect separately.
If you are planning to build a custom home in Las Vegas, you can hire Merlin Custom Home Builders.