first, select the deck and set the thickness (height) in the right pane --> say the height is= 12" --> write 12"--> press Enter in the keyboard
The deck elevation (as well as the floor, ceilings, etc) is always referred to the base of the deck of floor. So, if you wish the upper surface of the deck at elevation= 0" considering a thickness = 12", then the elevation of the deck will be= -12"
Important tips regarding floors, cutouts, etc --> To set the objects, floors, walls, etc at the right elevation, you need to define the ceiling heights. To do this--> Design--> Default Ceiling Heights--> set the exact height of each level. By default, they are 96", this means that (if you don't set your custom heights) Punch will set the second floor at 96" from the grass and the 3rd floor at 192" from the grass
--> The ceiling / floor / deck elevation is the bottom face of the ceiling / floor. This means that if you the floor of the second floor (for example) is @ 108", and your 1st floor has a ceiling of 12", the ceiling elevation will be 96" and the settings of the cutout (if you have one) will be the same: elevation at 96"and thickness= 12"
--> If you used a floor in the upper floor, you must consider this thickness in the floor cut
--> Say the elevation of the second floor of your house is 100", (using Default ceiling heights) so if you are working with the second floor of your house, you working elevation will be 100" . If you drag a drop a table on the second floor, by default, Punch will place the object on the floor, so in this case the object elevation will be also 100" . Now say that the height of the table is 40" and you put a lamp on the table, the object elevation will be 140" (100" to the floor + 40" to the top of the table) .