You can request longhouses by checking in online if you have a res linked to a
MDE account. I've done this twice: once requesting Fiji during Christmas week, the busiest time of year; and the second time, last October, asking for a specific floor in Aotearoa. Both times, I was granted my room requests via online check in. Christmas, we checked in very, very late at night. This past October, I checked in around noon. As I said, I got my room req both times, AND my room was ready during this past October's early check in.
You can also call or fax with longhouse/floor requests. And many others have mentioned that if you are 1) disappointed with the room assigned upon check in and 2) willing to wait until something else opens...the resort cast members will work to grant your requests.
That said...by next August, the vast majority of construction should be done, so it should not affect nearly as many longhouses as it has this past summer and fall.
If you want a room with great monorail views, my suggestion is to request GV Aotearoa with a balcony, which will put you on the third floor. The monorail facing rooms in Aotearoa are great, AND if there is construction going on in the middle of the resort (as we saw in October), Aotearoa is away from it. We were there in the middle of the construction when they were tearing down the volcano by the pool...and we were totally unaware of any of that construction while in our room or on our balcony in Aotearoa this past October. The room had great views of the monorail AND was removed from middle-of-the-resort renos.
Good luck!