I need a mechanical engineer

I am remodeling my condo unit. I am redirecting gas lines from 2 fireplaces to a tankless gas water heater and a dual fuel stove. I need plans drawn out from the main to the unit and to the 2 appliances. Also the size of the gas line and how calculation of how much the gas output will be.
I have no idea, how many hours will be needed to draw out the plans, and how much this project should cost.