Suprised this was not asked at CT forum.
Wages are very much a regional thing so what I pay may be too much for what you'd pay in Texas.
Paying piece work is totally lega, but carries with it a whole set of IRS rules. Hours must still be tracked and over time must still be paid. IMO better to pay hourly with a bonus tied into the piece work and/or on time/early completion.
Will this person work with you as a helper or unattended as a lead man?
How many workers on the crew?
How many feet would you xpect him to install in a day?
All of these factors would weigh in on my decision of what to pay.