Charging for Professional Services..building the model

Would love to hear from other folks who work in a hardware/software business and charge for professional services for onsight implementation services and project management work. How did you think about building the SOW/contracting, what costs were passed through to customers, and how is that structured in the contract, if the customer is using a 3rd party partner for some of the work and other work is being done by your internal team - any input on how to get started is appreciated.