I've seen them made out of old fridges, but they must be very clean inside, your going to need that heat lamp your on about, also you will need a fan of some sort to circulate the air a pc fan will do. But this will have to be 240v not 12, the heat lamp must be connected to a thermostat so it maintains the right temp, the fan can run constant but the heater must not.
Also apart from temperature you will have to consider humidity so your going to have to either get a hygrometer or sort out a wet bulb and a dry bulb thermometer and calculate the relative humidity from that. If the humidity is not right then I believe it can have serious consequence's on your hatch success.
You will also need to provide enough adequate ventilation so they can breath but at the same time no drafts or sudden temperature fluctuations.
Consider also that they need to be turned every few hours so that's going to be have to done manually, when they hatch they will also need light as well as heat. I don't think they need to feed for the 1st 24hrs but you will need to research this.
Thinking of hatching you must also give great thought and care to what substrate they hatch onto to help prevent foot and gait deformity.
You perhaps would consider cutting an observation window into the door so you can keep an eye on them with out opening and closing the door this will obviously need some sort of window pane either glass or perspex.
I don't think I can help you with the actual wiring of the thing due to legal reasons. But you must take care at all times to make sure it's safe and properly earthed.
But you really need to read up on and research this subject it's not as straight forward as it sounds
![happy :)](https://chat.allotment-garden.org/Smileys/green/smile.gif)