I am starting to rebuild Lego sets that I played with when I was younger. I know I don't have enough room in my bedroom to display all the sets I have, so I'll have to rotate them in and out preferably without taking them apart and rebuilding them.

Some of the larger sets I have:  7662, 8032, 7477, 8964, and 7671, anything else is relativity smaller than the at-ap.

What is the best way to store already built sets?

Disassemble them and bag the pieces in a zip lock, then box. They will stay much cleaner and you can always build them again if you want to change up your displays.

You'd need a large storage area if you were to store them built. And I'd guarantee they would't stay fully assembled,

Disassemble them and bag the pieces in a zip lock, then box. They will stay much cleaner and you can always build them again if you want to change up your displays.

That is what I would do. I'm in the process of disassembling many of the smaller sets that I have built over the years. I'm only leaving the larger sets built for now.

I totally agree with taking apart and ziplock bag approach.  Often times I actually grab the instructions when taking apart and go in reverse order and number the bags as I go so when I want to build them again it is almost like building for the first time.  

Okay, guess I gotta print out some manuals and get zip-lock baggies.

Lego has all the instructions available on their web site, just write down the set number and store it with the set. No need to print out 100's of pages of instructions.

I am starting to rebuild Lego sets that I played with when I was younger. I know I don't have enough room in my bedroom to display all the sets I have, so I'll have to rotate them in and out preferably without taking them apart and rebuilding them.

Some of the larger sets I have:  7662, 8032, 7477, 8964, and 7671, anything else is relativity smaller than the at-ap.

What is the best way to store already built sets?

I am on my phone so I have not checked what your sets are but I keep medium sized sets partially built in a box. For example, one box perfectly fits my VW camper van and the Mini Cooper. 

This method allows me to quickly change displays but not every set works and you will have to disassemble, or partially disassemble, some sets and store them in Ziploc bags as suggested.

Lego has all the instructions available on their web site, just write down the set number and store it with the set. No need to print out 100's of pages of instructions.

Didn't think of that, thanks

I am on my phone so I have not checked what your sets are but I keep medium sized sets partially built in a box. For example, one box perfectly fits my VW camper van and the Mini Cooper. 

This method allows me to quickly change displays but not every set works and you will have to disassemble, or partially disassemble, some sets and store them in Ziploc bags as suggested.

I will do that.