Pablo,
If you have a working system with Yosemite, you could reuse the same boot pack. Just need to change a couple of things in the Config file.
You need to disable SIP and change Smbios to MBA 6.2.
Launch Config.plist file with Clover Configurator, under RT variables tab, enter the following
BooterConfig = 0x28
CsrActiveConfig = 0x67
Then under SmBIOS, click on the magic wand and select MacBookAir 6,2.
See here.