Once you finish lavas at TH 9 your GG will inevitably reach 1 billion. Just upgrading legos and lavas by themself cost 1 billion total if you use all gold for upgrading them.
250 legos at 1 million a piece (250,000)
+250 lavas at 3 million a piece (750,000)
= 1 billion total loot (not necessarily all gold, but hopefully you get my point)
Then when you add in all of the other building upgrades it can easily get you to 1 billion gold grab at TH9.



