Sorry if I'm missing something here, I want to make a variant of the Goliath that normally doesn't have subclasses.  Making a "variant" doesn't seem to have the option to create subclasses.   Do I have to make a new homebrewed race based of the goliath or am I just missing something?

 As far as I know, sub races can't be created for variant races, probably because the official variant races don't include sub races.  (Most of not all official variants for races that didn't have subraces).  So yes, I think you will need to hombrew a Goliath or Goliath-like race.  Since you can "copy" the Goliath details (by using it as a template), that should be fairly easy.

Thanks for the response.  Follow up question.  I think it would make sense to just make it a variant with an ancestry option.  Like the Dragonborn.  Is there an easy way to make a variant,  get rid of 2 racial abilities so I can wrap them up into an ancestry option?  What I'd like to do is take the Mountain Born and Stones Endurance and wrap them up into an ancestry choice for Stone Giants.  then I'd like to have Fire Giant as another option that are acclimated to heat and get a fire based reaction.  and so on for the other giant types.  

You can use the Options to do that. The options would be called "Storm Born", "Fire Born", or whatever you decide.

Then you can make additional options that are granted automatically based on prerequisite selections

Note that you can't replace multiple traits with a single one

Steps would be:

• Make variant
• Add an ability "Giant Heritage" that replaces Mountain Born
  • Add an option "Fire Born" - this is the fire adaptation
  • Add an option "Storm Born" - this is a storm giant trait, hold breath or something like that
• Add an ability "Giant's Endurance" that replaces Stone Endurance
  • Add an option "Flame's Endurance" - this is your fire based ability
    • make sure to select prerequisite racial trait "Giant Heritage - Fire Born" and check the "is granted box
  • Add an option "Sky's Endurance" - this is a storm based ability
    • make sure to select prerequisite racial trait "Giant Heritage - Storm Born" and check the "is granted box

Oh sweet thank you!

That's a really neat idea!

Sorry that I don't have any advice to offer on the subject though. I'm just commenting so I can find this thread later on to see what results you've come up with.

:-)

Oh,  I appreciate the comment :)  I'm working on the variant now.   I was trying to give spells to some of the variants but doing that I won't be able to release it if I do that.  

Well here you go,  https://www.dndbeyond.com/characters/subraces/63678-goliaths-with-giant-ancestry ,  I'm open to feedback and balance.  something I considered was making the ancestry also change the +1 ability score modifier but thought that was a little much.   Fire Giants don't have a different climate resistance.  My logic for that is,  the fire giant would have been the only ones that were different,  the goliaths as a race live in the mountains, the MM says that fire giant's don't like it but they can become acclimated to cold climates.

Wicked cool! 

*Yoink!*