Depending on your State/County requirements your building will need to be issued a Certificate of Occupancy before you can live in it. Check with your local code enforcement officials before you start this project. Some code inspectors take a very dim view of unusual buildings or systems.
Some of the things you will likely need so you can live in your dream house:
A set of construction drawings with an engineers or architect's stamp. - This is the engineer saying the building is not going to kill someone once it is built. Getting a set of drawings for an existing train car may be difficult.
Code review of the drawings will required before you can start construction. Code review is required to make sure something did not get past the engineer. If the code inspector says you have to do something before he will approve for human habitation, you are going to end up doing it whether you like it or not.
DO NOT piss off the code inspector. The code inspector can make your life a living hell, if just by putting your application at the bottom of the pile and not getting to your application for the next 6 weeks.
Find out in advance what inspections are required, when and in what order. Nothing is more frustrating than having Inspector A come out and then finding out that Inspector B's sign off is required before Inspector A will look at the building. Nothing pisses off the electrical inspector finding all of the cover plates have been installed before he has inspected them.
Proper compliance for water and sewer connections.
Proper compliance for heating and ventilation requirements.
Proper compliance for insulation requirements- walls, roof and windows. From what I know about subway windows, those are going to fail and have to be replaced with code compliant windows.
A licensed, insured and bonded electrician. It is almost impossible to get past this requirement. The code inspector will not certify the building if he cannot be assured that it is not going to burn down because of bad wiring.
Installation of Natural Gas/Propane may require a licensed or bonded installer. Check with your local code inspector. There is a reason why the utilities inject the "natural gas" smell into the lines.
As my signature says: With construction you can only compile once.
Consider the drawings and specifications your program. All of the libraries that you load in as well (and must comply with) are the local and state construction codes.
You cannot undo your compile without a significant amount of time, effort and money. Make sure everything is behind the walls before you sheetrock.