Be wary of free plans sites as many are related to or spin offs of the infamous Teds Woodworking plans which is a rip off designed to do little more than take your money.
There are plenty of sites with free plans..
http://woodarchivist.com is pretty good with lots of free plans.
Another with lots of links to root around for plans and other general woodworking knowledge is
https://www.woodnet.net/links
I build a lot of furniture and other things made of wood, but most are from my own imagination or otherwise taken from other plans and modified to suit my needs.
Once you understand the basics of furniture or other types of construction you can modify just about any plans you might find online.
I'm preparing to build a cabinet to store both my wife's collection of different boxes of tea and our collection of coffee cups and mugs. I spent a good deal of time trying to find plans for such a cabinet, but none really fit the bill so I've modified it with a plan from finewoodworking.com and the rest from the stuff crammed between my ears.. It's made primarily from red oak and will likely weigh more than anything that will ever be stored inside of it...
The term "dammit, I can't remember the word" springs to mind. I had it right before I started typing it and have forgotten the term, but it basically means made to fit..
Anyway, learn the basic techniques and you can design your own furniture or anything else without the need for specific plans..
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