The first time I built a wheel a number of years ago was the first time I messed with truing wheels at all. I was in a bit of a pinch and didn't have much money after I wrecked my front rim so I bought a new rim and learned how to build wheels. This was of course without any of the proper tools except a spoke wrench. I used the fork as a truing stand and brakes and fingers to check for how true it was.
In the end I took it to my LBS to have it all checked out and it was fine and didn't need any adjustments.
Don't be afraid. There's really not much you can mess up. If you're a little unsure, take the wheel to your shop and have them check your work.