While TM has noted attic decking before, Infinite Attic is another contender in the race to make use of all that space you have in the attic. The structural aluminum Infinite Attic Saddles fit over 2×4 attic roof trusses; 2×2 rails (customer-supplied) fit in the saddles, and sections of 19/32″ plywood or OSB (customer-supplied) are attached to the rails using 6D nails or 1¼” long #8 screws. The $30 18-saddle kit will cover 32 square feet (lumber not included).
Unless your house is WAY bigger than mine, Infinite Attic is either hyperbole or a misnomer. I told them a billion times not to exaggerate.
Do you need more storage space in your attic? Or do you just need a way to prevent putting your foot through the ceiling?