Trying to remember...

Would Startopia be the game you're looking for?

http://en.wikipedia.org/wiki/StarTopia

The player is tasked with developing a series of space stations according to the wishes of various employers. The game is set after an apocalyptic galactic war, and many of the stations are in a state of considerable disrepair. It is hinted that these space stations are essentially the last few space-based environments available to the denizens of StarTopia, as most of them had been destroyed during the war.

The player has no direct control over the aliens that wander about the station. Instead, it is the player's job to construct rooms and hire aliens to staff them. The rooms provide basic necessities as well as recreation, encouraging visitors to remain on the station and continue spending money. Each type of alien is suited to a particular kind of task, and individual aliens have a set of statistics that determine their value as an employee. The actual goal for the player varies from one scenario to the next; in some scenarios, the player is expected to meet an economic goal, while in other scenarios the player is required to perform a specific task such as converting a certain number of aliens, or taking over the entire station by force.

There was another RTS that I had in mind, but this one seems to fit your description better.