Many of the bathroom vanity units have a look that hearkens back to older times, before houses had running water and people used wash basins.
These household utensils which are freestanding with basins sit on top of the bathroom countertop or whatever furniture piece is used to support it in the bathroom, however some models have the ability to be mounted on the wall, such as a wall hung vanity unit.
Meanwhile there are bathroom vanity units with basin on their top varied in model and color.
If you are adding a new vanity unit in as a replacement for an old bathroom vanity that is already in-place, you will want to contact a plumber to ensure that your pipes are properly located to fit the new sink.
Obviously, if you already have a countertop or vanity in-place you will need to have them removed in order to accommodate a proper installation of the new vanity unit.
Depending on the bathroom basins that you choose to used, you can opt to have fixtures and faucets installed either into the countertop or the piece of furniture used to support the basin, attach them to the wall behind the basin or even install them on the edge of the basin itself.
As to the color and size of your preferred setting,it should be up to the whole ambience and dimension of your bathroom.
No matter whatever scale of your bathroom is,there always are various models for your choice and several colours available.