This is not my model. It's from M6454 user of SketchUp 3D Warehouse, just made a render with Twilight Render.
Each Builder's Hut comes with one Builder which allows you to build and upgrade the structures of your base. You obtain two Builder's Huts from completing the tutorial, with another three available for purchase by using Gems.
You need Builders to construct and upgrade Buildings, Walls and to clear Obstacles. They are also required to place and upgrade Heroes. However, you do not need a Builder to place Decorations or Traps.
It won't be long until your Builders are spending 1-2 days or more on upgrades, so additional workers will come in very handy!
Your first Builder's Hut is already constructed when you begin playing the game for the first time.
The second Builder's Hut costs 250 Gems and is required to be built during the tutorial. It will use half of your initial allotment of 500 Gems.
The third Builder's Hut costs 500 Gems. There are generally two ways to acquire the third Builder's Hut:
500 Gems can be purchased for US$4.99. See the Gems page for prices in other currencies.
Save up 500 Gems by completing Achievements and removing Obstacles. You don't need to spend any Gems during the tutorial (other than buying the 2nd Builder's Hut). Saving 500 Gems from Obstacles and Achievements is actually not difficult; in fact there is an Achievement called "Sweet Victory!" (3 stars) which rewards 450 Gems, almost enough to buy the third Builder's Hut by itself.
The fourth Builder's Hut costs 1,000 Gems (you must already own the third). Buying 1,000 Gems would cost US$9.99.
The fifth Builder's Hut costs 2,000 Gems (you must already own the fourth). The required amount of Gems can be purchased for US$19.99.
It is possible to save up enough Gems to build all five Builder's Huts eventually, as there are a total of 6,312 Gems available via Achievements which means collecting all the Achievements will give you enough Gems. Also, there is an unlimited amount obtainable by clearing Obstacles such as plants and rocks (plants regrow every 8 hours).
Defensive Strategy
You can put your Builder's Huts in the very corners of your village, in hopes of wasting opponents' time getting to them when attacking - which might mean the difference between a 2-star defeat instead of a 3-star one. However, the drawback of doing so is they will be easy pickings for a single Archer or Barbarian, and each building (regardless of purchase price or hit points) counts the same amount toward 50% destruction.
Builder's Huts can be used like Walls or other buildings to push back the no-spawn zone of Troops.
They can also be used to lead enemy troops a more desirable direction (for the defender). Because units with no preferred target simply attack the next closest building once they have destroyed their current target, you can strategically place Builder's Huts to ensure that these troops find a string of closer buildings leading away from high-value targets such as Mortars and Air Defenses.
Offensive Strategy
Attackers should look for Builder's Huts or other buildings in corners and may combat this by placing one or two Barbarians or Archers at each building at the start of a battle.
They can also use those corners to lure clan castle troops without the lone archer being picked off.
