I noticed on the last page of the tower crane plans, there is a stacking plan for the 16-story version of the building that includes the heights. Granted it's only the stacking plan, but it is meant to show the general scale of the building and the floor-to-floor heights.
The 16th floor is listed as 210 feet, and the roof, which is certainly only the main roof, is listed as 225 feet. Each of the floors are 14 feet tall. Now, we all know the building was approved at 19 floors by the board of regents. So it should be a good bit taller. Assuming the design depicted in this stacking plan compared to the final one approved is the same, the the height to the main roof should end up being 267 feet. I would estimate the mechanical penthouse is around 10 to 15 feet more. So the mechanical penthouse and top height should be somewhere around 277 to 282 feet.
By the way, the shorter of the two cranes is listed as 284 feet to the top of the peak of the crane. The hook height is listed as 252 feet. So the top of the crane is 37 feet above the hook height. The tallest crane for some reason is listed as 228 feet, which must be some kind of typo, because it lists the hook height as being 291 feet. 291 feet plus 37 feet is 328 feet. And for a ~282 foot tall building, it wouldn't be unreasonable to think that it would need a 328 foot crane.
ftp://ftp.ci.austin.tx.us/ATD_AULCC/...rane_PLANS.pdf
Also, don't worry about it being scaled back, because that crane permit shows a date of April 14. We only found out it would have 19 floors near the end of August.