Walls for wardrobes and storage rooms

[klintan]

In the process of building a house, and for some closets, I am planning to frame partition walls, either just to create a niche or perhaps in some cases to create a walk-in closet. Under the stairs, I've also planned to build a storage area in the same way.

Can this be done on top of the interior floor? Are there solutions so that you don't need to drill holes in the interior floor in that case?

Or should these walls be constructed before the floors are laid?

Under the stairs, there are tiles, and in the bedrooms, there is oak laminate flooring.

 

[Larsa]

I see no problem with building on top of tiles. However, there might be some issues with the wooden floor since it needs to be able to move.