Programmatically how to create site collections in SharePoint

Method 1: 

In this method first i will create new web application and then create first site collection in that web application.

            try
            {
                int port = Convert.ToInt32(txtPortNo.Text);
                string UserName = txtUN.Text;
                string DBName = txtDBName.Text;
                string ServerName = txtServerName.Text;
                string SiteCollectionTitle = txtSiteCollectionTitle.Text;
                string SiteCollectionDesc = txtSiteColDesc.Text;
                string SiteColOwner = txtSiteColOwner.Text;
                string SiteColOwnerEmail = txtEmailAddress.Text;
                bool isAvail = CheckPortUsage(port);
                if (isAvail)
                {
                    SPWebApplicationBuilder builder = new SPWebApplicationBuilder(SPFarm.Local);
                    SPWebApplication newApplication;
                    builder.Port = port;
                    builder.ApplicationPoolId = "SharePoint - " + port.ToString();
                    builder.IdentityType = IdentityType.SpecificUser;
                    SPFarmManagedAccountCollection manaccountcollection = new SPFarmManagedAccountCollection(SPFarm.Local);
                    SPManagedAccount maccount = manaccountcollection.FindOrCreateAccount(@UserName);
                    builder.ManagedAccount = maccount; //use the SPManagedAccount to receive the username and password automatically
                    builder.RootDirectory = new System.IO.DirectoryInfo("C:\\Inetpub\\wwwroot\\wss\\VirtualDirectories\\" + port.ToString());
                    builder.CreateNewDatabase = true;
                    builder.DatabaseName = DBName;
                    builder.DatabaseServer = ServerName;
                    builder.UseNTLMExclusively = true;
                    newApplication = builder.Create(); // Create new web application
                    newApplication.Name = "SharePoint-" + port;
                    newApplication.Provision();
                    SPSite mySiteCollection = newApplication.Sites.Add("/", SiteCollectionTitle, SiteCollectionDesc, 1033, "STS#0", @UserName, SiteColOwner, SiteColOwnerEmail);
                    mySiteCollection.Close();
                    //display message like "Web Application and site collection Created Successfully"
                }
                else
                {
                   //display message like "Port Not available"
                }

            }
            catch (Exception ex)
            {
                //show the exception
            }



 public static bool CheckPortUsage(int port)
        {
            try
            {
                new TcpClient(new IPEndPoint(IPAddress.Any, port)).Close();
                return true;
            }
            catch
            {
                return false;
            }
        }


Method 2:


Creating site collection under root web application i.e '/' if already root site collection created then it will through an exception
            SPSite site = null;
            try
            {
                SPWebApplication webApplication = null;
                webApplication = SPWebApplication.Lookup(new Uri("http://ukreddy:8998"));
                site = webApplication.Sites.Add("/", "firstsitecollection", "sitecolection desc", 1033, "STS#0", "UKREDDYSYKAM\\administrator", "UKREDDYSYKAM\\administrator", "s.urkeddy@gmail.com");

            }
            catch (Exception ex)
            {
                //Display error message.
            }
            finally
            {
                if (site != null)
                    site.Close();
            }


Method 3:

If the root site collection is already created then above method through an exception like " ".
Then need to create new site collection under managed path i.e /sites/


            SPSite site = null;
            try
            {
                SPWebApplication webApplication = null;
                webApplication = SPWebApplication.Lookup(new Uri("http://ukreddy:8998"));
                site = webApplication.Sites.Add("/sites/siteCollname", "sitecollectiontitle", "sitecolection desc", 1033, "STS#0", "UKREDDYSYKAM\\administrator", "UKREDDYSYKAM\\administrator", "s.urkeddy@gmail.com");

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
            finally
            {
                if (site != null)
                    site.Close();
            }