If the pentominoes are made using cubes instead of squares (so that they have a 'thickness' of 1 cube) then it becomes possible to work with 3dimensional shapes. The simplest problem then is to put all 12 together to make a cuboid. Clearly it will have a volume of 60 cubes.
It can be done as a 3 by 4 by 5; or a 2 by 5 by 6; or a 2 by 3 by 10. All of these are possible.
8 of the solid pentominoes can be assembled to make a twicesize representation of most of them, but it is NOT possible in the case the I, T, W and X.
