Is there a way to build walls up properly. I want to build tall but without floors.
I haven't tried this and it makes no sense, but I'm pretty sure it will work:
Build your structure to the height you want with floors in it (at least around the inside of the walls at each storey) and then remove the floors.
The building would collapse in reality, but buildings in FO4 can't collapse. You can have entire buildings suspended in midair by building them on foundation blocks and then removing the blocks, so a floorless tower of thin shack walls should be fine.
Using a similar method, you can put buildings through things they can't go through, e.g. a tree. Build the whole building on a foundation block (or two, or however many you need for the required height) a distance away from the tree, then group select the block (hold down E with default PC controls) which will select everything attached to the block. Move the whole thing to the desired position, put it there and then remove the block(s).