In terms of time, I would say weeks. Human to Vacuum cleaner, your "losing" mass, and transmuting chemicals, which takes minutes. So sizing up to something like a space shuttle, weeks is probably a minimum.
I would also have your player making concentration checks, say every 4 hours. He can eat normally during the early stages, but after that, no he doesn't have to eat.
If he blows the concentration check, the result should be equal to the mass he's gained. The farther along the path he is, the more likely he's swimming through 2,030 TONS of ectoplasmic goo.
2,030 TONS. Oh my, oh my, oh my. What a huge amount of fun that could be. If you assume 6 weeks for the transformation, it's 338 tons by day 7. 48 tons per day on the six week schedule. Heck, for that much fun... start the difficulty low, and build. You really want the balloon to pop at 48 tons (1,920 CUBIC FEET, 13,440 GALLONS) or more....
Another entertaining option, is that the mass is coming in the form of ectoplasm from the NeverNever. I wonder what creepy crawly is going find the hole, and say "Hi!" that everyone is going to have to deal with.
Which brings me to the fuel question, he doesn't eat fuel. Vacuum cleaners don't eat dirt. They need to be plugged in. If he actually wants to lift off, he's going to need to generate the fuel as well.
Which brings to all the reasons why NASA uses gantry's to hold up the shuttle. It's one great big huge sail standing there in the wind.... which could bring a whole lot of hilarity on it's own.
Also, don't forget that as the shuttle takes size and shape, it's going to have to deal with some of the things the current shuttle does. I seem to remember nesting wood peckers and other bird issues. As in pecking holes in things and building nests.
Then, you have what happens when the engines light off. That's basically a controlled explosion going off. That could be entertaining to explain, because the cops, FBI, Secret Service, FAA and every other alphabet soup agency in the government is going to want to know. THAT's probably 10 or 15 different story arcs all by themselves. Being able to pull this off at the cape, or other authorized launch site... probably not possible. Even so, there's no way to keep the launch secret.
If the character is a shuttle engineer, maybe it'll actually fly. The parts are highly complex, and all have to work perfectly. Getting the plans and designs and know how to do this, would be interesting in and of itself. You can kind of fake your way through being a vacuum cleaner, but this is in a whole new galaxy of complexity compared to that.
Something else to think about, at 48 tons per day, that's 2 tons per hour. That's a veritable whirlpool of ectoplasm coming out of the NeverNever. What happens if something gets caught in that? Since NeverNever beings are ectoplasm, it would be reasonable to assume that whatever gets sucked into the vortex becomes a part of the shuttle.
Now, if that happens to be some sort of phobophage. Let's face it, the shuttle is a flying bomb, space is horrendously dangerous all of which will raise the level of fear, which would feed the phobophage of course. Power struggle for the flying ship of fear between the changeling and the phobophage? Sudden leaks in the ship? I can imagine so many ways to turn this into a wonderful campaign all by itself.
What if it's something a little more fire oriented? In a flying bomb? Or something with a vendetta against someone? Now they're fighting for control of the shuttle. Maybe a hunting party from one of the Faerie courts? Or a raiding party, and you get both sides?