How to create multiple sites at Plone with seprate add-on?

When i am trying to setup a new site As a result it creates a new site with existing project so please help me How can i create a new Plone independent site.I am using Plone ver 4.3.x ?

You are not very clear with the expression "new site with existing project".

If an "add-on" is designed properly, putting it into an environment does not directly affect any Plone site. To get an effect on a site, you must do something special. This "special" thing often is installing it via "portal_quickinstaller" or the "plone control panel" into the site. It may also be inheriting the site specific skin (often called "IThemeSpecific") from the add-on skin.

Thus, if you observe that an add-on affects a newly created site without extensions (they are means to include "add-on" during site creation), then likely the add-on has not been properly designed.

You need to tell us more details about your "add-on"s and the bad behaviour you observe in order to get better help.

@dieter "add-on affects a newly created site without extensions " exactly this is my problem so what to do for resolve this issue ?

Please be specific and give details about Plone versions, add-ons etc...otherwise nobody can help.

@zopyx Plone ver 4.3.3
and i created my own egg project so whenever i am trying to create a new site without pick my egg but it affects a newly created site and as result it give me same site

As I tried to express in my previous reply, this means that your add-on (which likely means "your own egg project") fails to address an important design issue: having no affect on a Plone site unless explicitely installed in this site.

The "Zope component architecture" makes it difficult at some places (e.g. for "subscriber"s) to get this effect - but for other aspects, its facilities are quite good. For example, most views (and other "request" multiadapters) can be restricted to specific environments via the "layer" registration attribute.

Usually, "Add-On"s have (to quite a large extend) no effect on a site unless explicitely "installed" into this site (either via an extension during site creation or lateron via "portal_quickinstaller"/the "plone control panel"). Your "add-on" fails in this respect. You will need to provide a lot of detailed information about this "add-on" and what precisely goes wrong that we have a chance to understand why this happens.

I got my answer actually i created plone-addsiteTemplates files that was overriding the core Plone files and thanks @dieter to provide me some inputs from your side