we have directional antenna(internet) placed on top of 5th storey building. will the device work properly. pl

Depends on what you are trying to do. If you are trying to connect to a distant AP which is within the line of site, it will work just fine.

If you are attempting to use it as an Access Point from inside the building, it wont work too well.

The only limitation height wise is if you "overshoot" your intended target it will have a poor performance. Or if you have way to much cable from the antenna to the radio and and loose all the signal in cable loss.

There is only three main things you have to worry about when broadcasting a wifi signal.

1. Line of sight being unobstructed.

2. The power of your broadcast and received signal.

3. Radio interference between the two antennas.

I have broadcast and received a signal with 2 Cantennas 1800 ft with no problem.

http://www.cantenna.com/