The idea is that the board has 2 hoverpads which cause it to hover, provided energy from the box in the center.
This is one of the ideas for the hoverpads
>>1117
The dimensions for the size of this hoverboard are as follows;
Length: 70 cm or 27"
Width: 18,8 cm or 7.5"
Depth: 2,5 cm or 1"
Regular cd/dvd/blueray disc size could be used for elements inside the hoverpads. Given that idea the size of such a disc is 12 cm in diameter. The aluminium plates are about 17 cm wide. so an idea for the cover for the hoverpad could be 16 cm diameter on the outermost edge, middle slant could vary and the inner ring could be 12 cm diameter. The sketch in the pic has a side view of the cover for this idea.