Of course you can but will it work and is it strong enough to take the forces applied to it without breaking off the hub are the questions you should consider.
A steering wheel can be made out of anything round, or square, or any shape as long as it is within the same size as the original and will operate in the same movement range a normal steering wheel has.
Here's what you do:
1) Get an aftermarket steering wheel hub for your car, momo is a good one
2) Take a piece of paper, make an outline of the hub, then poke holes where the screw holes are on the hub into the paper (your template)
3) Place template as centered as you can onto your desired steering wheel then mark the holes.
4) Drill holes into the center part of the wheel you want to use to match the holes on the aftermarket hub
5) Attach the hub to steering column first using center locknut, then screw on the wheel you just made to the hub
...and you're done. This is the same method you have to do when you buy a brand-new untapped racing steering wheel, same process. It will work.