Create a subsite programatically and add SPGroups

SPSecurity.RunWithElevatedPrivileges(delegate()

{

using (SPSite osite = new SPSite(siteCollectionUrl))

{

using (SPWeb oweb = osite.OpenWeb())

{

SPWeb site = null;

site = oweb.Webs.Add(Weburl, projectname, projectdescription, EnglishLocaleId, sitetemplate, true, false);

site.Navigation.UseShared = true;

site.Update();

isSitecreated = true;

if (isSitecreated)

{

site.AllowUnsafeUpdates = true;

site.SiteGroups.Add(site.Name + "-Owners", site.CurrentUser, site.CurrentUser, "");

site.SiteGroups.Add(site.Name + "-Visitors", site.CurrentUser, site.CurrentUser, "");

site.SiteGroups.Add(site.Name + "-Members", site.CurrentUser, site.CurrentUser, "");

SPGroup gOwners = site.SiteGroups[site.Name + "-Owners"];

SPRoleAssignment assignmentOwner = new SPRoleAssignment(gOwners);

assignmentOwner.RoleDefinitionBindings.Add(site.RoleDefinitions["Full Control"]);

site.RoleAssignments.Add(assignmentOwner);

SPGroup gVisitors = site.SiteGroups[site.Name + "-Visitors"];

SPRoleAssignment assignmentVisitors = new SPRoleAssignment(gVisitors);

assignmentVisitors.RoleDefinitionBindings.Add(site.ParentWeb.RoleDefinitions["Read"]);

site.RoleAssignments.Add(assignmentVisitors);

//Add users for visitors group

//gVisitors.AddUser();

SPRoleDefinition roleDefinition = site.ParentWeb.RoleDefinitions.GetByType(SPRoleType.Contributor);

SPGroup gMembers = site.SiteGroups[site.Name + "-Members"];

SPRoleAssignment assignmentMembers = new SPRoleAssignment(gMembers);

assignmentMembers.RoleDefinitionBindings.Add(roleDefinition);

site.RoleAssignments.Add(assignmentMembers);

 site.AllowUnsafeUpdates = false;

}

 else

{

  isSitecreated = false;

 }

}

}

});

 This will help you to create site and groups programatically