One of the top grossing strategy games in playstore as of today is the game called Clash of Clans.
Even I myself got addicted to it after a couple of weeks. I found out that one of the most necessary
building a player need is the builder. You can buy builder using gems.

Builder Cost
1st Builder Free
2nd Builder 250 Gems (Required to buy because its part of the tutorial)
3rd Builder 500 gems
4th Builder 1000 gems
5th Builder 2000 gems

Gems are somehow expensive, you can buy 500 Gems for $5. Not all of us wants to spend real money to enjoy something. So I've got this guide for you that can help you buy all 5 builders without opening your wallet(Except for the monthly electricity bill or the internet fee rofl)

First, Clash of Clans give 500 gems to as you create your town. Then, you are to buy the second builder as you go through the tutorial.Viola, now you have 2 builders and 250 gems remaining.

FRIENDLY TIP: Save your gems. Keep it until you're able to buy every single builder that is available.

Now, press the achievement button on the bottom right part of the screen, there you'll see the achievement button. (A villager's face)

Scan through it and you'll see the number of gems as a reward for completing a certain task.

One of the most easiest task is the Sweet Victory. You need to fight other villages in multiplayer battles for trophies.
75 trophies will grant you 5 gems, 750 trophies will give you 10 gems. 1250 trophies will give you 450 gems.

Then you'll be able to purchase your 3rd builder.

Another easy achievement you can do upon reaching Town Hall level 6-7 is the League All-Star. You'll be rewarded gems as you go through higher leagues.
Crystal League which needs 2000 trophies will give you 250 gems. Masters League which requires 2600 gems will give you 100 gems. then the Champion League which needs 3200 trophies will give you 2000 gems.


TIP: You can do this fast if you stock up golds and elixir, then go to multiplayer battles, Find a village that has their town hall outside the defenses or in the corner, focus on destroying the town hall then end battle. You'll gain trophies without even spending too much armies.
Repeating this can make you reach Champion League in a week. After that, you can now buy all 5 Builders.

There's also a free GEM BOX every week which contains 25 gems.

Sounds easy right? Now go ahead and get those builders!



Sources: 
Achievements: http://clashofclans.wikia.com/wiki/Achievements
Trophy Leaguse:http://clashofclans.wikia.com/wiki/Trophy_Leagues
Builders:http://clashofclans.wikia.com/wiki/Builder