Create a SharePoint Content Type programmatically

using (SPSite p_site = new SPSite(urlToSite))

{

    using (SPWeb p_web = p_site.OpenWeb())

    {

        SPContentType CustomContentType = new

                SPContentType(p_web.AvailableContentTypes["ParentContentType"],

                p_web.ContentTypes, "MyContentType");

        // A string Field

        p_web.Fields.Add("NumberColumn", SPFieldType.Number);

        SPFieldLink fLink1 = new SPFieldLink(p_web.Fields["NumberColumn"]);

        CustomContentType.FieldLinks.Add(fLink1);

        // A required number field

        p_web.Fields.Add("StringColumn", SPFieldType.Text, true);

        SPFieldLink fLink2 = new SPFieldLink(p_web.Fields["StringColumn"]);

        CustomContentType.FieldLinks.Add(fLink2);

        //A Choice Field

        p_web.Fields.Add("ChoiceColumn", SPFieldType.Choice, false);

        SPFieldChoice choicefield = (SPFieldChoice)p_web.Fields["ChoiceColumn"];

        // Add a group to the filed

        choicefield.Group = "MyGroup";

        // Add choices

        choicefield.Choices.Add(string.Empty);

        choicefield.Choices.Add("Yes");

        choicefield.Choices.Add("No");

        // Set the default choice

        choicefield.DefaultValue = string.Empty;

        choicefield.Update();

        SPFieldLink fLink3 = new SPFieldLink(choicefield);

        CustomContentType.FieldLinks.Add(fLink3);

        p_web.Fields.Add("LookupColumn", SPFieldType.Lookup, false);

        SPFieldLookup lookupfield = (SPFieldLookup)p_web.Fields["LookupColumn"];

        // Set the remote lookup list

        lookupfield.LookupList = new Guid("guidofremotelist");

        // Set the remote field

        lookupfield.LookupField = "remotefieldname";

        lookupfield.Update();

        SPFieldLink fLink4 = new SPFieldLink(lookupfield);

        CustomContentType.FieldLinks.Add(fLink4);

        CustomContentType.Update();

    }

}