Hi, I've been using a Samsung 840 Pro 512GB ssd for a couple of years now, but I wish I had a bit more space for games, instead of buying a larger SSD, can I buy another 500GB ssd, I'm thinking of the Samsung 750 EVO 500GB ssd, they are about $129 right now.  Can I put them both together in a RAID and reinstall windows on that?  Technically one ssd is 512 gb and the other newer one is 500gb, but hoping it could work so I could double my hard drive for cheap, your thoughts?

There is a way in windows so you can just expand the drive to the new drive. So when the one drive runs out, it just moves onto the new drive. Known as a Spanned Volume.
Otherwise, RAID 0, you will be limited to the smaller drive. So for a better example, if one drive is 120 GB, and the other is 500GB, you will only have a 240GB RAID 0. Also if one drive fails in RAID 0, you WILL, lose ALL data without chance of recovery.
Setting up a RAID 0 will require a reformat.
 
If I am wrong in any of this, I'm sorry. Been a very long time since I have bothered with any of this type of stuff.

I think you are correct. I have 4 x Samsung EVO 250GB SSD in raid 0 only for games. If one drive fails, I lost my game installs. My OS runs on a single SSD drive and usually the savegames are stored in your home directory or in the cloud, so if the ssd array fails, I can reinstall the games when I rebuild the array replacing the lost one.

As discussed above, if a drive fails with RAID 0 you'll lose all of your data and won't be able to rebuild the array.

RAID 0 is a striped volume, not spanned.

I'm not a pro at all of the other RAID types either - I just referenced several different websites.
 
OP, for your options - https://www.prepressure.com/library/technology/raid
 

 
Or just install it as a 2nd drive (D:) and reinstall all your games, Steam etc. on there.. that's how I have mine set up.
 
 

Me too.

C: 240 GB SSD, D: 4 TB HDD, E: 512 GB SSD

Same here. C:/ is a single SSD, D:/ is a RAID0 of 4 SSDs. I only install games on D:/ unit.

Ditto.  OS is on an SSD and the entertainment drive is 2 Raptors in RAID 0.
 
Were it me, I would simply add the 500GB SSD to the system and then migrate all the games and saves over to that drive.