Yeah, when you're trying to select wall and floor colors in build mode, it can be a bit dark. What I do is just keep adding light fixtures until the room lightens up enough for me tell what it really looks like. I move them around too if I need to. When I've gotten things the way I want them to be, then I just delete any lighting fixtures that I don't need for live mode. Adding windows temporarily helps sometimes too, to give you more light to work by. And I find that using the afternoon setting works better for me for most of my builds.
Hope this helps.
This is what it looks is that what yours looks like too?
