Building large buildings in DF is unfortunately tedius. You need to do some construction designations, unpause, wait for them to finish, do more designations, unpause, etc., and you need to do it in the right order or else your dwarves will will get stuck or be unable to access a corner. Completely fixing this problem would probably be quite involved, but perhaps there is something that could be easy to do and would help a lot.
Right now, dwarves can access fruit in trees several Z levels above the dwarf using stepladders. Also right now, if you build a stair, a dwarf can place a construction directly above it without needing to be on the z-level of that construction. How about let dwarves use stepladders to be able to reach constructions above them if they cannot otherwise path to it?
Optionally, you could potentially then allow players to define constructions without existing support nearby; it just won't be a job any dwarf will take until support is built adjacent to it. Of course, when you build a construction it must path to find what resources are available to be used -- this could just start on the nearest ground below said construction. This could let you define more constructions in one go, reducing the tedium of making large constructions. I say "optionally" because even if designations operate exactly how they do now it would still be very useful.
I only make this suggestion because I figure it would not be hard to implement, since the functionality appears to be already in the game. And I think that it would make for a very significant improvement. If I am wrong and it would be difficult to implement, I understand.