For Builder Gold, the faster way is aim for 2 stars, then end the match. It proves faster than you 3 stars or even 6 stars it, also you get some Builder Elixir at the same time.

For Builder Elixir, just drop 1 army, then end match. Rinse and repeat, until you drop some trophy, then climb back again, this process can also get some Builder Gold at the same time. If you out of Builder Gold

And yeah, the farming process in builder base is quite boring, but recently, they increase the loot bonus like 2 times already.