Stagger Your Builder Upgrades 1 to 2 Days Apart
As you are upgrading your defenses, plan ahead and look at the current upgrade times before starting the next upgrade.
If possible, attempt to stagger your upgrade finish times so that they are around 1 to 2 days apart. This gives you enough time to save up the required gold or elixer, but also prevents you from being in the situation where you have maximum loot and no builders to spend it.
If you are not playing as much you can adjust the 1-2 days to the amount required to fill your storages.