Dallas’ much-praised Morton H. Meyerson Symphony Center turns 20 years old next month, and one of the people behind its success is EDS founder Ross Perot, who ponied up $10 million to build the place. During an event at NorthPark Center last night to announce a Sept. 12 gala marking the Meyerson anniversary, the diminutive billionaire recalled an early exchange he had with I.M. Pei, the symphony hall’s world-renowned architect. Perot noticed that some of the center’s ceiling tiles were cut at different angles, and he asked Pei why. The architect replied it was because he wanted the ceiling tiles to match the floor tiles exactly. “Who would ever notice that?” Perot asked. Replied Pei: “I will!” To which Perot said: “Well, you are I.M. Pei–and I am ‘I Will Pay.’ “