500
The default Imperial template measurement between levels is 10'-0". You have 3 levels, Level1 , Level2, and Level3 currently at 10'-0". You want to edit the height for Level1 to be at a height of 12'. Do this.
What is select Level2, Level3, and Level4 using Ctrl or a Window selection from right to left touching each Level you wish to select.
• On the Options Bar, click the "Activate Dimensions" button
• In the temporary dimension that appears between Level1 and Level2, type 12'-0", then ENTER