60x40 area (feet I assume)? Potted plants? Sounds like a nursary.
Post a scale drawing of the layout and you might get some suggestions. Even if it doesn't, you'll still need a scale model to give to a professional to design it for you. Do a Google on words like "irrigation design" and you should find companies (like Rainbird) that will allow you to submit needed information and they'll design the system for you.
