I am working on a decking and carpeting project now and have read every post on this site (some more than a few times). From what I have read, most people agree that 1/8" is enough room to allow you to tuck or roll your carpet. However, don't forget that the carpet makes the storage lid sit up higher, so when you have it all done, the lids will not be flush with the deck. (Think about it, if the lid sits flat, but then you roll carpet around the edges, it no longer sits flush)
You can fix this in 2 ways...I think. I read another member used 1/2" plywood for the deck, and then 3/8" plywood for the lids. I was also considering for my project that if you are framing the deck and then cutting the lids flush with the inside of the frame, you will be adding 1X2's as lid supports on the inside perimerter of the whole. Simply put the lid supports 1/8" down. This would be cheaper than buying seperate sheets of different sized plywood. Then again, we're also considering not wrapping the carpet and using trim instead.