Don't buy pre-built! Many manufacturers (Mavic, Cane Creek, some Campagnolo, etc) use proprietary spoke lacing/hub flange systems that make it extremely difficult for a novice or anyone who doesn't have the proper tools at the time to do roadside maintenece or even to replace a spoke if given a little time. Not to mention, these wheels are often built by machine and never truly equilibrated, thus lending to quicker out-of-trueness than a wheel built by a master.