A picture is worth a thousand words.

It is not built yet, so no picture. It is a minds eye question.

Construction drawing?

Where is the architect on this?

Well a bit early then to plan the soffit if you only have drawings IMO. Some things just really do not lend themselves to finish before build . I aslo think your architect designed the house ask them

Pretty difficult to answer without any images. But I don't think I've ever seens a soffit with board and batten, so would suggest some contrasting material to the siding.

We have a grey house, black windows, black frames, black posts etc and we have wood soffits. J forget the type of wood but I love it. Here is a pic but it’s dark

That looks really good! Thanks for the helpful comment!