eg. I would've made for a bad lawyer. conveying the meaning that if I had been a lawyed, I would have been a bad one. is it correct usage?
One of the uses of make when used in this construction is be suitable for. Check it out in OALD.
I've never heard this expression used with the preposition for. The expression should be "I would have made a bad lawyer".
EDIT: Following Fumblefingers' and Lynn's comments, I found the phrasal verb make for something, which means help to make something possible (from the OALD entry for make. The example cited is "Constant arguing doesn't make for a happy marriage."). I cannot find evidence that this usage can apply to human potential. I insist that "I would have made for a bad lawyer" isn't accepted usage.
In a nutshell, yes, "I would have made for a bad lawyer" means that you would have been a bad lawyer if you had become one.
However, as the extended comment trail on the other answer attests, there are some regional (and perhaps personal) preferences on whether to use the word 'for' in that sense. I see these two statements as equivalent:
The first is more idiomatic to my AmE ears. I have seen the second more commonly in BrE uses (books, TV). But even in AmE, one commonly uses made for to speak of inanimate objects/concepts: