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You'll need to keep the camera perfectly level unless you're using a tilt shift lens. If you can't, you can replicate the effect without a HUGE loss of quality if you just gently tilt the lens down and allow some extra room to skew it in photoshop.
there was also a TON of barrel distortion to correct, that was probably the hardest thing - Im not sure what lens you used but wooo it was a killer

and it's not perfect, but it's better.
there are tons of ways to clean up barrel distortion, but it's important to make sure the walls are perfectly straight. take some rulers in photoshop and skew/drag/warp it around until they're arrow-straight.
I did some random cleaning around too. This is totally polishing a turd, haha, but you can make it look a lot better by just cleaning it up like this.