In case you didn't notice, there's no Wizard or spells in Builder Base. Without a Wizard, there's no one to brew spells. Everything comes from the master builder, like the Battle Machine.
At some point we think Supercell will add spells to the Builders Base, we're just not sure when. This would be a huge change to the overall balance and game mechanics for versus battles. If they can figure out a way to make it work, we want spells. In fact, I think we need spells. Unfortunately, this first big Clash of Clans update in 2019 will NOT add Builder Hall 9 to the game, sadly, but it is coming eventually.
The best idea I've seen so far is a Revealer Spell. This would be an expensive spell you can use in the Builder Base attacks to see Tesla's, bombs, and traps. Then, plan your attack accordingly.
Another one is a "Targeting Spell" where we can direct any and all troops to specific targets for a small amount of time, like 10 seconds. This would mess up the mechanics of attacks and funneling, so it's doubtful. That said, the AI in the Builder Base is pretty bad, so a target spell would really increase the effectiveness of attacks. Or, we'll just get some of the same spells we already have, like healing or rage.