Haven't you lived together at all until now? If not, then living together in your wife's apartment offers the opportunity to first find out exactly what your future house should look like. Building a house should really be planned thoroughly down to the smallest detail, otherwise you'll be annoyed later when planning mistakes have been made everywhere. Kitchen planning must also be included from the very beginning; the room dimensions must fit the kitchen requirements and not the other way around—planning a house first and then somehow fitting a kitchen into it later. This goes on in every room: where should the room be located (direction), how big should it be, how many windows, how large, etc. Most people spend a few months on this. It is actually irrelevant whether you live longer in an apartment beforehand; a baby doesn't need its own room yet, much more important is a house that you are satisfied with later and above all a construction company that you have carefully chosen. Our first apartment was not even 40sqm and we lived there for 1.5 years; it never felt too small to me.
Best regards
Sabine