Not at all If you want to build a floating structure just make a nice connection with it through a portal (I suppose you'll want to enter it someway ), but you're not limited to that at all.
If you can do that, don't build it exactly by the road like
beacause it will leave some kind of dead area below your plot, leave a 2 plot space for other people builings by the road and good luck!
PS Guildelines are just guildelines. You can build your floating structure any way you want.