SSD not selectable for Yosemite installation
Are you booted from another drive or Internet Recovery and, if so, are you able to repartition instead of erase the disk using Disk Utility?


Select the drive in the Sidebar
Select the "Partition" tab
Change the "Partition Layout" to "1 Volume" (or however many volumes you wish the drive to have)
Click "Options" and change the partition map to "GUID Partition Table" and click "Okay"
Name the partition whatever you would like and set the format to "Mac OS Extended (Journaled)"
Click "Apply"


If everything went according to plan, you should be able to install Yosemite from the OS X installer. If not, you can try my solution posted here to sort it out via Terminal.