We've got a home that doesn't really work for us anymore and renovations were going to be incredibly expensive so are looking at a knock-down rebuild option. More money, of course, but also a better result.

I've engaged with a moderately large off-the-plans builder as a starting point as they offered a high degree of customization even when starting from an existing plan (I won't name them at this point).

They offer a whole bunch of standard things for the build, but most of the detail is somewhat vague until you sign the build contract, which I don't want to do until I'm happy with everything.

We've made significant variations to the standard plan we started from, but I'm pretty detail-oriented so I was hoping to say something along the lines of...I have a maximum budget and would like to get the best house I can for that money, so make tradeoffs in design and spec in "real time" to maximise the quality for our purposes. That process doesn't really seem possible given the way they work, because there's a sales guy between me and all of their internal people (drafting, QS, etc.). So all I can really do is ask for modifications and of course they'll just say yes and do it, with results back in about a week.

Is what I am wanting simply not feasible with an off-the-plans supplier? I went that direction because it seemed easier to start with an initial idea, but I may have hamstrung myself.