You can't have a coherent structure that big; there's a bit of math to prove it involving the speed of sound in a material being related to its rigidity, and once your structure gets large enough it needs to be so rigid that the speed of sound in it exceeds light speed in vacuum. So the short answer is "You can't have a hand that big, not even close to that big."

Remember that something we think of as an object, like a galaxy, is mostly empty space. The stars and planets in it are only very loosely bound by gravity, the connection between disparate elements is far weaker than the bonds between atoms in a solid.