In my line of work I hit a few deadbeats (fortunately very few, about 5 or so the last 10 years).
I use what I call the "power of positive annoyance".
Be nice, but never give up reminding them of their debt. Mail a statement to him every month, adding your contract late fees/finance charges each month (your contract stated that, right?). Email him weekly. Call him every once in a while, but be nice. Don't harrass, just ask nicely when your check is coming. Or be a little more vague -- he'll know what you are after without you saying it. Find out where he eats lunch, just happen to run into him...don't say much other than "hope to hear from you this week..."
I got a check once for an account that was about 3 years out. Guy told me he'd never had paid it but I was there every time he turned around.
To many small business will give up within 2 or 3 months. Keep at it.
Be careful about collections laws, though...but as long as the debt is owed to you, you can do many things that can't be done if you sell the debt or have a collection agency handle it.
Then again, builders are a whole different critter. Good luck.