would be a cool conversion... i kind of like the beetle, would be cool to do that to a metro.
hard to fathom how that sort of mod would be street legal anywhere. it most certainly wouldn't be over here.
how about looking for a cheap (metro) convertible... with the roof in a bad condition for example might not have to much miles either as it's more of a fun car... the frame should already be strengthened so you'll just have to fair over the passenger seat, shorten the windshield and create teardrop roof. in fact you might do away with the windshield altogether and build something like the top of a record recumbent bike or small airbplane... a fiberglass dopshape with an aircraft style windshield.
while you're at that you could give the car a "nosejob" as wel
you could even make it so that you can convert it back into a two or 4 seater when the need calls, with detachable panels or hatches, some sort of jeep style windhield that fold backwards to cover part of the pasenger compartment but giver the extra pasenger some sort of wind protection.
it all depends on how dedicated you are and it'd cost more than running a standard striped out metro of course.