You don't have to name the flooring, you know. A least from my experiences you can just not name it, and it seems to stay unamed like the rest of the tiles until you connect it to something, like the shed. Or you can build from a flooring tile next to the shed flooring, and it will assume it's part of the shed and never ask. That is how it looks like it works to be anyway, but that was from several releases ago, so it's possible things could have changed since.
I personally like using graph paper to map out the squares onto the page, lightly filling squares for nearby buildings, roads, bridge, waterline. Then go around the property and see where I can and can't build any structure and map out the border of the property. Then I plan out the building design, walls doors, windows room layout and furniture. I surprisingly find it fun to do, and I suppose it also fits my character's lore as a carpenter/builder, so I tell the NPCs I'm "surveying" the land and "drafting" up build plans if they ask.