When you start playing Clash off Clans, you begin with 500 gems. By the end of the tutorial, you end up losing nearly 50 gems by completing structures instantly as instructed by the tutorial. If you instead save your gems, you will be able to add extra builders at a quicker rate.
Here are the costs for each builder:
Builder 2: 250 gems (you add this during the tutorial)
Builder 3: 500 gems
Builder 4: 1000 gems
Builder 5: 2000 gems
While builders 4 and 5 are a long ways off, builder 3 is achievable relatively quickly if you save your gems. Extra builders allow you to construct more buildings at once and as a result are very helpful. With the new Clan War achievements and a trophy push, you can unlock the 4th builder within a few months of playing even without purchasing anything. The 5th builder will require a major Trophy push (to Champion’s League) or more time to unlock some of the other achievements.