I would suggest to start from something existing as modifying is (to me) always simplier than entirely scratch-building.
Maybe the ST185 Celica light pod ?
Usually plastic card and putty are your best weapons, some use metal but I can"t help with metal...
I also used in the past (especially when building figurines or wargames parts) modeling clay hardening on air to get the shape but it's not always strong enough for scale models...
I hope this helps...
