I was wondering what the maximum vertical height is for endgame in spin up.
There is no vertical expansion limit.
Take a look at SG5 in the game manual. @Arronax is correct but there are some protections in the goal area.
d. There are no vertical expansion limits during the Endgame.
e. Robots may not contact the High Goal, Discs which are Scored in the High Goal, or the horizontal supporting structures directly underneath the High Goal. This rule applies at all times, regardless of Alliance / High Goal color.