Should I build risers and treads out of hard wood floor pieces
Time = Money. And assembling these in a manner that won't cause you headache later is going to take a lot of time.

To make a tread, you'll need to laminate the floorboard together somehow, otherwise they will flex under the weight. Construction adhesive would work, but wood glue might be better. And don't forget to sand or plane off the finish before you glue them together because the glue won't stick as well to the finished face.

Multiply all of this by the number of steps you have.

Another method with slightly less work is to put down regular stair treads, then put your hardwood planks over the top. You need to carefully select the correct thickness of the tread, taking in to account the thickness of your planks and the nose molding. This is similar to what is described in the article you linked to in your comment.