Actually I don't know what's wrong with plain old concrete. This is a very standard flooring for aviaries, and it's supposed to be easy to clean. The site at
http://www.bluequaker.com/Art-034.htm says "A concrete floor is the easiest to keep clean, requiring only frequent hosing and an occasional wash with a mild bleach solution. Care must be taken to provide adequate drainage when electing for concrete." Then they go into detail about the drainage. My sister used concrete flooring for dog kennels, and as far as I know all she did to clean it was squirt it with a hose. Dog poo is obviously a lot more heavy duty than cockatiel poo and she had big dogs (huskies).
BTW that site says they used a peaked (gable) roof. I would expect that any type of sloped roof will make the water go to the side. The shed roof makes it go to one side and the gable roof makes it go to two sides. I don't know all the issues with drainage but you could ask him if it makes a big difference.
The other standard alternatives to concrete are dirt/grass or sand/gravel which have more cleaning issues. I've never heard of using tile in an aviary before. It sounds cool but I don't know how well it works. I don't know whether this guy has previous experience with aviaries but you could mention to him that concrete is commonly used and tile isn't. I haven't looked into tile in detail, but if you google for aviary floor tile you do get some results. So I'd suggest checking it out to see what people say.
This board lists some pros and cons of concrete:
http://www.ausbirdforums.com/viewtopic.php?f=39&t=577Here's a simple article with some nice tips:
http://www.idealhomegarden.com/outdoor- ... an-aviary/ One of their suggestions for flooring is to use cement blocks, which I haven't heard of before. Seems to me that those would be prone to tilting if it wasn't done just right.