We have a walk in attic that is only has a small area which is finished. Would 1/2" plywood be sufficient to finish out the rest of the attic for use as a storage area (no living space intended)?

At a minimum. Might feel a little bouncy but will get the job done and be easier to work with.

I wouldn't use plywood, look at using OSB (waferboard) instead.

I'd go with at least 5/8". As was said, 1/2" will work, but will be bouncy.

Another thing I have done is use 1x3 scabbing boards. About the same price per sq/ft, but you can do the job yourself. Also easier to get a 8' board that's skinny in openings and around parts than a single sheet. Comes in 3/4" thickness.

Just my experience and thoughts. Also helps out if you have to get to a section under it. Unscrew a couple of planks and you still have a working space.

~egon

at home depot, they have plywood sheets that are specifically used as flooring for attics. They sheets come in a manageable size and have grooves so they fit together. I believe they are 5/8 in thickness.