You can always add borders until it is large enough.
PatriceJ is correct is that most blocks can be drawn on a grid.
For example, the star block you have pictured is on a 4x4 grid.
If you wanted to make it a finished 16x 16 block, the center square would be 8 inches (cut 8 1/2), the corner squares would be 4 inches (cut 4 1/2), etc.
If you wanted to make it a finished 8x8 block, the center square would be 4 inches (cut 4 1/2), the corner squares would be 2 inches (cut 2 1/2 etc.
You could do it almost any size you want, but I find it easier if I keep the bigger pieces in even number multiples - or at least no smaller than 1/2 inch increments.
That particular block would be easy to change by two inch increments. Even number multiples.
A twelve inch block works well for many designs because 12 divides evenly by 2, 3, 4, and 6.