How to use Builders
First you should get the third builder right away when starting clash of clans. This will help a lot. Then use gems moderately, mainly just using them for 1 gem boosts. By town hall 7 it is a good idea to be really saving for the fourth builders hut, as upgrades take more time. Now onto how you should actually use them. Early on, I try to get my collectors/mines maxed fast, as this helps get the gold and elixir you need faster. 1-2 builders huts can be dedicated to this at first. As you get further in the game, only use one builder on this. At this point (TH7) it is good to have 1-2 working on defenses, and any other builders huts working on army camps, and barracks. Extra elixir you have can be used in the laboratory and gold on the walls. Constantly upgrade everything, and try to have one builders hut focus on the short upgrades, while one does the long upgrades, and the other for whatever is needed. Your base will start to max out quicker this way. Finally, while it would be ideal to ma out every townhall, you often need better troops, or better collectors/mines to do this. That is why I would suggest halfway maxing out most townhalls, until 7 when you start fully maxing out your townhalls. 7 is good for this because of good troops, and max collectors/mines unlocked. Clash on!