Builder hall 5 is where you unlock the builder machine (BM), currently the only hero in the builder base. It is a unique hero compared to the main base, because you can reuse its ability multiple times, regenerating health each time it is used. You can use the electric hammer once per 15 seconds and it increases damage for 3 attacks. Like the main base, you only unlock his ability at lvl5 so you need to get him there to get full use of him.

You need lvl30 BM to unlock the OTTO who is the 6th builder on your main base. Having him means that you can max out TH12 faster. You can also use him as your second builder in the builder base which is mostly useless because you are gated by resources in the builder base, not builder time.

BH5 is also where you unlock cannon carts which is also one of the requirements for the OTTO. This will be the second troop you upgrade along with barbs. They are decently strong and barb + carts can push you to higher leagues even up till BH9. However, they are basically useless until lvl10 so you don’t need to worry about them until later on. While you will unlock them now, you will probably only be able to use them at BH7/8.

Builder base 5:

You have a lot of competition in elixir usage here because the BM and lab both cost a ton of elixir. Upgrading barbarians would mean that you can bring 60 barbarians into your raids instead of 40. However, that costs 2.2mil elixir and 3 long upgrades. After doing the math, it seems that getting lvl1 BM is the better option initially then you need to save up and upgrade your barbs to lvl10. Barbs to lvl10 is better than BM to lvl5 so we’ll focus on that very soon.

1. 2nd elixir storage. You cannot build or upgrade anything meaningful until you upgrade this. You need at least lvl4/3 storages to build your BM.
2. Battle Machine lvl1. He still doesn’t have his ability yet, but that’s ok. With him, you can easily push another 100-200 trophies and gain more loot.
3. All new walls, new push trap, new spring trap, new mine, new firecracker, new double cannon. Build everything that is cheap and fast to quickly increase your strength.
4. New gold mine and elixir collector to lvl3. This is a good balance between cost required and loot generation.
5. 2nd gold storage to lvl2. This allows you to store more loot, that’s all.
6. Star lab lvl5 or multi mortar lvl1. Depending on how much gold and elixir you have, upgrade your star lab or multi mortar. After one is done, do the other.
7. Once star lab is done, upgrade barbarians twice to lvl10. This will greatly increase your power, allowing you to 3 star almost all BH5 if you have the skill.
8. Elixir collectors to lvl5. Max them out so that you can produce more loot per day.
9. Elixir storage to lvl5. This will allow you to store 1.5mil elixir
10. Gold mines to lvl5. Same reason as above
11. Gold storage to lvl5. You need this to store enough gold for the BH upgrade.
12. (optional) Try to squeeze some time to upgrade your builder barracks to lvl7. This will allow you to start upgrading cannon carts.
13. (optional) clock tower lvl3/4 and gem mine lvl1/2. Just upgrade these if you have extra loot/time
14. Builder hall 6. Upgrade now so that you can rapidly increase in strength. Going to BH6 quickly will allow you to gain more trophies than trying to get BM to lvl5 right now.
15. (optional) upgrade cannon carts to lvl2 or bomber to lvl3/4 if you have excess elixir while waiting for BH6. These are quite expensive upgrades, so just upgrade these if your elixir is going to overflow. Try to bring 1.5mil elixir into BH6

Builder hall 6:

BH5 didn’t offer much in terms of upgrades except barbarians. Now, you can quickly gain more strength to get more loot per day. This will make previously expensive upgrades much easier to do. While it is tempting to do some catch up here, you can get another army camp and barbs increase in numbers at BH7. This means that BH6 is just a simple layover. BM lvl5 becomes cheaper here because of the increased loot power. In BH7, you cannot get the army camp as early as previous BH, so getting BM lvl5 is still a better use of elixir for now.

1. New walls, new archer tower, new mine, new mega mine then new crusher. This will greatly increase your defensive strength and probably stop the 60 barb spam against your base.
2. Battle machine to lvl5. Doing the math, upgrading him is more worthwhile than upgrading barbs to lvl12. This will cost 4.6mil elixir while barbs cost 3.2mil. Barbs don’t gain much in these two levels while BM will allow you to take down crushers that enemies have. We are upgrading him
3. Upgrade elixir collectors in between BM upgrades if you cannot afford the next upgrade or if your gold is overflowing.
4. If gold is constantly trying to overflow, do some quick 5-60 minute defense/trap upgrades before starting BM upgrades so that your gold will not overflow. You can also upgrade some walls too.
5. Star lab lvl6. This will allow you to upgrade barbs to lvl12, which is basically just to prepare them for lvl14.
6. Barbs lvl12. Save up elixir and upgrade barbs once you have
7. After barbs are done, upgrade barracks to lvl7 if not done so previously.
8. Gold mines to lvl6. Increase your passive income
9. Gold and elixir storages to lvl6. You will need both maxed in preparation of BH7. Elixir storage is especially important later on, because your 5th army camp will cost you 2.5mil elixir
10. Builder hall lvl7. Get there asap and you will unlock 100 barbs soon enough.

BH5,6 are just transition periods because they don’t have army camps and you gain so little strength that it really is not worth it to stay here for too long. Once you reach BH7, you may want to “catch up” on some stuff because you don’t gain strength as quickly in BH8/9. Everything in the builder base is about opportunity cost. Sure, you can upgrade BM to lvl5 in BH5, but you can do it easier with extra defenses in BH6. Likewise, you can spend the time to upgrade cannon carts in BH6, but why do that when you can just rush to BH7 and get 100 barbs in your army for a fraction of the price?