how old is this building?

Bu bina ne kadar eskidir?   (kaç yaþýnda?)

(modified)

You can leave out the ´kaç´, Sonunda!

I´d started to write kaç yaþýnda then changed my mind but left the kaç in by mistake!

I wasn´t sure about the ´kaç yaþinda´ because I thought it was just for people not things.

how old is this building?

Bu bina ne kadar eski?  
Bu bina kaç yaþýnda?
Bu binanýn yaþý kaç?

teþekkürler.Every body.

It is not correct to say "bu bina kaç yaþýnda" because it is not a living thing.

"bu bina ne kadar eskidir" is correct and also you can say "bu bina kaç yýllýk(týr)?"

That´s what I thought earlier-thanks.