AUBURN — A roomier, newer and more energy-efficient terminal at the Auburn-Lewiston Municipal  Airport should put a nicer face on the entire area.

“This is the first place a lot of business leaders see when they come here,” airport Manager Rick Cloutier said. “We’ve done what we can with the building to clean it up and keep it nice. But it’s still a 50-year-old building, and that shows.”

Engineers are expected to finish construction designs for an $800,000 addition to the terminal. It will make more room for the Landing Strip Cafe and fixed-base operator Twin Cities Air Service. It also will create an office for U.S. Customs officials and add a waiting room for pilots and their passengers.

Designs call for using the existing space, adding a new roof and building the addition along the southern side. It doubles the size of the airport’s building, from 3,500 square feet to 7,000.

Cloutier said he hoped construction would begin in the summer of 2011 and wrap up later in the year.

“Basically, this gets us even with our needs today,” Cloutier said. “We’ve grown enough in the last few years that we are pretty much bursting at the seams.”

The airport’s 2006 master plan study estimated the airport would see an average of 72,000 takeoffs and landings by 2011. It’s on pace to have 75,000 takeoffs and landings in 2010. It’s also the home base to 120 aircraft — 30 more than the master plan estimated for 2011.

“We got there a little faster than the master plan expected,” Cloutier said.

Airport traffic has increased as much as 30 percent over the past five years. It includes air shipping and delivery service, but Cloutier said much of it comes from corporate traffic. The airport logs 500 trips from corporate airplanes each year, bringing in officials from TD Bank, Proctor and Gamble and other national companies with Twin Cities branches, as well as companies considering expanding into Central Maine.

“For a lot of them, this is the first experience they have with the Twin Cities,” Cloutier said. “What we’re planning will certainly look more inviting.”

The new design will leave room for possible passenger air traffic if that becomes an option. Part of the entrance could be set aside for passenger screening.

Cloutier said the next step for the airport is adding 1,000 feet to the airport’s Maine runway, making it open for larger aircraft. That project is being studied and designed. If federally funded, work would begin in 2012.

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