You want a "custom" home without the hassle, but buying a home that's already being built has advantages and drawbacks. Here are some considerations before making your decision.
Choosing to build a house from stock plans or from an architect's custom design requires vision, no matter how good the drawings are.Buying a house that's under construction gives you a chance to walk through the house (even if there's little more than framed walls and plywood floors) and get a sense of the layout. You can also see how the exterior is shaping up.
If you're moving into a new area or have other time constraints, you may be unable to wait the many months it takes to develop a home from initial planning to final construction. A house that's already being built can slash that time dramatically.
Building a custom home can be extremely rewarding and even enjoyable, but the process requires your involvement. Think about how much of your effort is needed to find and purchase a lot, choose or develop an initial design, tailor and change the design, find a contractor, monitor the construction, and choose the finish materials. A home that's partly complete eliminates many of these steps plus some of the risk. You'll also have a better grasp of the final price tag.
Some prime sites are purchased by builders for speculation houses. By purchasing a home that a builder is developing, it's possible to gain a more desirable location than you would have found for your custom home. However, your siting options are far greater when building from scratch.
When building a custom home, you can choose from any one of thousands of designs on the market or you can opt to work with a host of architects or designers. A house already under construction limits the changes you can make. The earlier you buy, the more changes you can make, but you'll also have to invest more time. Before you buy a home that's already being built, ask if the builder is agreeable to your customizing ideas.