Dreaming of a Fresh Start

In a distant dream world of bank loans, I fantasize of gutting my house and starting a new. It’s only 400sq st per floor (currently 3 floor with basement) and would like an additional two. What is the likely span of these costs (anywhere from basic to higher end) I would just likely to a number in my head, because I really have no concept of what the costs are for small home owners as opposed to the big developers with this type of undertaking. Anyone gone through the process, and have any advice, or referals? Obviously this is the wrong time to start this kind of project, but you have to start somewhere, and it never hurts to ask.

Thanks for your time.