“Builders have popular plans for a reason. They can build them cheaper and the home functions better. Ask the builder which plans they like and then ask them ‘why’?”
You should always ask the builder not only what plan they like – but why they feel that way.
Over time, all successful builders have found a plan (or several) with efficiencies in material use (means they can build it cheaper), contains features that people like (means it will resell better) and their subs know how to build it (built better AND faster.)
These are good things.
Likewise, be careful about too many modifications of a builder’s plans. Most plans are in their 4th or 5th iteration of redesign. The most popular plans have been built many times and thus improved on both the drawing board and in the field. Years of feedback from the Realtor community and home owners means that the flow is better and the home is well balanced.
What may seem like a benign modification in one room can impact another quite harshly and you end up with unintended consequences. This is not to say that you should not have input, just that you should be mindful that everything in a home in highly interconnected. Every inch you borrow from one room comes at the expense of another.
I have always found it helpful to get the builder’s take on what they do well because it usually a benefit to you.