Built-a-lot 4: Power Source is a resource management game developed by HipSoft and published by WildTangent, Inc. It is the fourth installment in the Built-a-lot game series and was first released on August 12, 2009. The gameplay is similar with the other Built-a-lot games wherein the player builds, upgrades, and sells houses in order to earn profits.
The only difference in this installment is the inclusion of another game element – the Power Source. The player must consider the available power generators when building and managing the neighborhood. The player must ensure that the available power generators are capable of handling all the houses or other infrastructures in the neighborhood. If the player fails to do so, the neighborhood goes into a blackout, in which he cannot collect any rent from the buildings.
There are three game modes in Build-a-lot 4. These are the Main Campaign, Challenge Campaign, and Expert Campaign. The Main Campaign has 45 levels while the Challenge and Expert Campaigns have 10 levels each. The player can only play the Challenge campaign if all the levels in the Main Campaign have been completed. The Expert Campaign will only be unlocked if the Challenge Campaign is completed. There is also a Tutorial mode, where the player can learn all the basics of the game. It consists of three levels only. For each level, the player must complete a set of goals. The player cannot proceed to the next level without completing the previous one.