Kathie, here are several videos, from building your own storage to buying the heavy plastic storage boxes and cabinets. I've looked at them at Home Depot, Lowe's and Ace Hardware. They are kind of pricey!
There are storage boxes made in thick weatherproof plastic and which have a seating area on top for around $100. They last for many years and can be locked if needed.
Hi kathie here is a link with a bunch of ideas
Have you thought about purchasing a large bin to store your cushions? I have one on my deck, I store the sunscreen, candles, matches and cushions in mine... it's a life saver when it rains.
It is important that patio storage be rain and windproof, fade resistant, low maintenance, and easy to clean. The opening must be large enough to accommodate your cushions and whatever other objects you want to put in or take out, in order to be conveniently accessible.
Yes, Suncast type resin bins may seem pricey at the onset. However, they are sturdy and durable, (I have had one for over 15 years). Most come with handles, and some have wheels, which facilitate moving even when full.
Considering the cost of all necessary materials, hardware, and tools to create your own patio storage, purchasing ready made quality may be more cost effective in the long run.