Official Q&A: VRC 2019-2020: Tower Takeover

when in autonomous, I know robots cannot cross the center line and touch the gray tiles or cubes on the other side - what about the airspace above the gray tiles?

Please review the Q&A Usage Guidelines, specifically point 3, "Quote the applicable rule from the latest version of the manual in your question.". Often, you'll find that by quoting the rule, you'll answer your own question.

Rule SG2 reads as follows:

<SG2> Stay on your side in Autonomous. During the Autonomous Period, Robots may not contact the foam tiles, Towers, or Cubes which are on the opposing Alliance’s side of the Autonomous Line.

Violations of this rule will result in the Autonomous Bonus being awarded to the opposing Alliance. Intentional, strategic, or egregious violations, such as intentional contact with an opposing Robot while completely across the Autonomous Line, will result in a Disqualification.

Note: Towers and Cubes which begin the Match in contact with the Autonomous Line are not considered to be on either side, and may be utilized by either Alliance during the Autonomous Period. If attempting to utilize these Towers or Cubes, Teams should be cognizant of the possibility that opponent Robots may attempt to do the same. <SG7>, <G10>, <G11>, and <G12> will be taken into account when these types of Robot interactions occur.

There is no rule prohibiting contact with the airspace above the gray tiles. Therefore, this is legal.