seem very sound as you have them. You are wise in the 2x6 rafters with that 10 foot span. If you can attach the rafters with metal fasteners that would be good also.
Since your joists are going to be 16OC (on Center) then you could use a lighter plywood decking. If your budget is straining, then you could take those joists to 24 OC and still be ok. With a tight budget or conserving $$ I would use the OSB stran plyboard. It is 1/4 inch thick but very strong. Those sheets sell for about $5 a sheet. If you don't think that they are thick enough, then double up.
Have you considered since you are building this storage area, about hanging a decending attic door. This would make getting up there easier and you can encorporate the stairs into your joists plans.
Keep us posted on your project for any problems that occur during the construction process and we will be happy to assist you.