Best way is take them out and keep them for your new build.
If you like, you can plug in the SSD to show your buyer that the PC works when you are selling it, then unplug it again
OK, and do you have the license key?
If not, and you have not yet wipes the PC....download this: Belarc Advisor
This will (hopefully) report your license key.
Then...after you have wiped all drives, boot from that USB and install.
Give the new owner that license key.