Matt, First thing you, as installer (in any way), and your customer as GC, have to do is comply w National Electric Code (NEC) 2008. All electric work has to be inspected by the local authority within the project jurisdiction. You can't get C of O without passing electrical inspection. "The Code" gives you minimums for location, spacing, and # of outlets, switches, lights etc, as well as placement of wires within walls, beams, panels etc. The code is extensive and thorough, and it really is all about SAFETY. Nice to have the record during construction of locations and your methods - it will be helpful to tradesmen or next house owner for future work if it isn't lost or forgotten about. Also maybe helpful if inspector makes you "open it up" or tear out non-compliant installation. Conductors (romex, bx etc) installed behind 1" nominal wood panelling must be protected with "nailproof" steel plate or be installed inside metal conduit no matter how well you map & mark its location and hope for NO NAILS.
Is your customer cheap or unrealistic? wants to have trouble w inspection beauracracies and doesn't worry about an electrical fire? Are you taking on work that isn't good for you? Homeowners insurance policies deny claims coverage for damage from uninspected, non-compliant electric work. I suggest you convince your customer to hire a licensed electrician and work with local authorities to be code compliant. You'll prob enjoy your part of the TF, carpentry and enclosure work more than your frustrating and probably illegal electric work. Work with your inspectors, in most cases they appreciate that. They are there to help make a good and safe job happen. I won't say good luck 'cause there is no luck involved in this one. Heads up! Be smart, protect yourself and your customer, and all the future occupants of this house.
Remember to protect the TF from wild drillers! See my recent post in tools forum on "drills...."
Take this as a friendly "Stop Work Order" before you get a hostile one!
Steve