Is it asking for disk space or an installation disc?
Are you using Galaxy or manually download the patches?

Are you sure that you are asked for a disk and not for disk space?
If you want to install patch 1.07 you need about 7,5 GB free space on drive C (it is the location of the windows temp files). If you haven't enough space try to delet or move some files from drive C or move your temp-folder.

Edit: For more information and how to solve the not enough disk space problem read this:
http://www.gog.com/forum/the_witcher_3_wild_hunt/patch_claims_not_enough_disk_space_but_there_is

its asking me for a Disk. i have 300gb free space on my C: drive.

That is weird. Did you bought the Witcher 3 on DVD? If yes try to install patch 1.02 first (this is the activation patch).

nope.. bought it digitally. this is the first patch ive had a problem with.

Hmm.... You could try to reinstall the game. But don't forget to backup your savefiles (just in case).

Here, I pulled this solution from the Witcher Reddit. Someone else had the same problem you did:

"Hey I was having the same problem and managed to find a fix.
The game temporarily copies the files over to your TEMP variable path which is on your C: drive. To change this path right click on 'Computer' --> choose 'Properties' --> 'Advanced System Settings' --> Environmental Variables. Then change the TEMP and TMP paths to a new folder on the drive where you have enough space and restart your computer.
I managed to run the patch .exe after this without any problems, hope it works for you!"