How to store a percentage value?
It depends a little on how you plan to use the value, but typically a decimal would be a good choice for storing percentages. And note that you could store it as the percentage value (10.01) or as the fractional (.1001). So that would affect the actual size and precision of the column.
The choice between storing as a percent or fraction depends on the usage needs, but I suspect that in most situations it would be simpler to store it as a fraction (e.g., .10 to represent 10%) because it can be used directly in most calculations more easily (don't need to remember to divide by 100).
And as @ismaelga points out in the comments, a decimal is a good choice for accuracy (particularly nice when dealing with monetary calculations).