For the last 10 years or so, we've covered our outdoor furniture on our patio. First we removed all of the cushions and put them in contractor garbage bags, not closed to allow for air flow, and placed them on top of our riding lawnmower in the shed. In other words, they are off of the floor.
Then, we group the furniture together, making sure there is a peak in the middle, think teepee. The grouping is about 4' tall. The chair/sofa covers remain on the pieces. Then we cover with a 20' x 20' outdoor tarp. We chose a dark green, almost black, one. Run a piece of rope in and out (weaving from the outside of one, into the inside of the next) all the way around the bottom of the furniture pile. Cinch the rope and tie in a knot. Tuck under the excess to keep leaves from entering underneath. The air flow comes from underneath, as well. It has worked wonderfully for us. If there is snow that accumulates on the top, we simply brush it off with a broom, occasionally. Make sure to uncover as soon as the snow melts to avoid any undue mold, etc. Besides, you'll be ready for spring at that point! Enjoy, and Happy Holidays!