Reward buildings are buildings in SimCity 4 which are not available by default, but need to be earned beforehand. While there are also non-reward buildings which need to be unlocked, no reward buildings are available in the beginning of the game and in most cases, only one of each building can be constructed in the city.
When the player unlocks a reward building, the city planner (Neil Fairbanks) will notice the player, as well as offer the player to build it in most cases. The player can turn down to offer, however, although it can be found in the reward buildings menu.
The reward buildings can be classified within two groups:
Business deals will not by default appear in the list. They are only available if the player is rapidly losing money and going deep into debt.
Shortly said, it is not recommended to build them. While they do net the player some money, they have adverse side effects which can ruin the city, as well as reducing the mayor rating. On top of that, they cost a lot of money to demolish.
Reward buildings have mostly positive effects when built. While some cost a lot to maintain, others are free and therefore highly recommended to build as most usually raise the demand cap.