Finished size will be twice as big, but that doesn't go for cutting instructions. If you're using HST's, QST's, strips, etc. the seam allowances for the finished cut are already built in, and they're not always 1/2".
I'm not completely clear whether you mean that you want to make each block twice as big, or whether you want to make the quilt bigger by making more blocks? Also not sure what you mean by twice as big - to cover twice as much area, or to be twice as big in both length and width (which covers 4 times the original area).