It would help to know what kind of room are we talking about, what is it used for and what are the materials? Is this a cafeteria or something?
Hard wall surfaces - and other surfaces too - reflect sound, making it echo. You want to add stuff that doesn't reflect soundwaves so much.
There's plenty of commercial products out there to improve acoustics. There is a cheap material called "woodwool cement board" aka WWCB, that looks like this:
http://www.apionet.or.jp/~e-eishin/img/p04-1.jpg - it's also lightweight and fire resistant and can be painted with normal house paints and still has the acoustic properties. It looks pretty nice when painted.
Also there's some gypsium "acousto-board" products out there if he wants a different kinda look, but these are more expensive than WWCB.
What I would do is make a ceiling and perhaps some wall surfaces out of WWCB, and look into adding some soft furniture like a couple of sofas and chairs into the space to "suck out" the echo, if possible.
