a tarp and duct tape?

dude, im telling you that custom will be more expensive than pre-made. Not only do you have to pay for labor to put on like a pre-made, but you also have to pay labor to have the material cut and sewn into the shape of the top. Custom hard top will only be more expensive because you have to have something to get the shape, or again pay for metal and someone to weld and fab it. Then comes the hardware required to fasten the top to the car. And don't forget body work and paint to make it look cute.

You may get more opinions from NICO Convertible forum, heres the link 240SX Convertible Forum: Nissan Forums / Infiniti Forums - NICOclub, but as much as it may not seem like it, pre-made soft top will be best and cheapest way to go.