I want a switch for NSIS installer through which i can made installer silent install with progress bar shown.For completely silent install it is /S but i want it for silent install with progress bar shown.Do anyone know this?

there is no such thing by default.
If one wanted a progress bar, you would have to modify the installer to add a progress bar page if there is a specific command line switch used.

And how can i made custom installer if there is no method of doing thhis.Where are the experts?Nobody know this answer or don't want to tell?

you sounded rude asking like that. maybe nobody knows or if someone knew maybe your way of asking scare him...
you can try to look in the NSIS documentation online to see if there is a way you can achieve what you want. as far as i know for standard setups there is no way to show progress bars...

I wrote a lot of NSIS installers and as I think there is no way to do it without modifying .nsi script.
And there is no way to extract this script from NSIS compiled exe.

I can suggest you to look at my signature.

P.S. You can try to ask it at NSIS forum (at winamp.com)