Whenever I actually get around to building my next airship, this tool will be extremely useful for planning and assigning purposes. I ought to try this out. I mean, with my last one, I was building it the hard way with the 10-tile limits, and expansion from supported contacts (making measuring and precision a bitch to deal with). This ought to make building such things, and other structures a crap-ton less stressful/tedious/annoying. Plus, now I can better-manage building projects with this tool, instead of having to find the right time to get things ready and etc.
Of course, this now brings up another idea you could implement: A function to mass-assign the construction tasks, be they to work on, or to suspend them by designating in a similar manner (or pre-assign construction tasks as suspended or not (especially good for when you don't want certain builders to trap themselves when constructing). You could say, regarding the amount of tiles assigned (be it furniture, walls, or floors) to a project, that's alot of hovering over all those tiles and hitting 'S' to temporarily suspend the tasks of all those parts; and I suppose, while we're at it, have that function also clear out the task (deleting the designation) so we can do similar, especially if some of us would maybe want to add a colorful mural in a floor or something, carve out a negative, and only the empty space will be filled with the new material assignment (since it's not overwriting the assigned material previously placed).
EDIT:
Just noticed your furniture planning plugin. Cool stuff you made here so far. Really practical. Haven't used them yet, and I already love them. Can't wait to try them out and continue my other forts.