How to Create Office 365 Website using Client Object Model ?

Let's cut to the chase. Here's the code below:

/// <summary>
/// Creates the child site.
/// </summary>
/// <param name="parentSiteUrl">The parent site URL.</param>
/// <param name="adminUsername">The admin username.</param>
/// <param name="adminPassword">The admin password.</param>
/// <param name="newWebsiteInfo">The new website information.</param>
/// <returns>a <see cref="bool"/> indicating if the site was created with success or not</returns>
bool CreateChildSite(string parentSiteUrl, string adminUsername, string adminPassword, WebCreationInformation newWebsiteInfo )
{
    // by default assume the function will fail. Just to be on the safe side.
    bool output = false;
    try
    {
        // create a clientContext from the provided parent site
        // and get the collection of all the webs below the parent site
        ClientContext clientContext = new ClientContext(parentSiteUrl);
        WebCollection currentListOfWebs = clientContext.Web.Webs;

        // encrypt the password in a secure string and add to the current context
        SecureString password = new SecureString();
        foreach (char c in adminPassword.ToCharArray())
        {
            password.AppendChar(c);
        }
        // add the credentials to the clientContext. This will avoid the nasty 403: Forbidden errors.
        clientContext.Credentials = new SharePointOnlineCredentials(adminUsername, password);

        // create a new web object using the websiteinfo provided
        // and add to the collection to make sure it is under the right parent
        Web newWebsite = currentListOfWebs.Add(newWebsiteInfo);

        // execute the web provisioning
        clientContext.ExecuteQuery();

        // if got to this point then it was executed with success
        output = true;
    }
    catch (Exception exception)
    {
        // something went wrong, add to the ULS, display some message etc...

    }
    return output;
}

Then what you have to do is to call like in the example below:

/// <summary>
/// Handles the site provisioning call
/// </summary>
protected void ProvisionSite()
{
    WebCreationInformation webCreationInfo = new WebCreationInformation()
    {
        Title = "This is my new child site",
        Description = "This is the description of my new child site",
        Language = 1033,
        Url = "childsite1",
        UseSamePermissionsAsParentSite = true,
        WebTemplate = "STS#0" // team site template
    };
    CreateChildSite("https://<yoursite>.sharepoint.com", "<admin>@<yoursite>.onmicrosoft.com", "<your password>", webCreationInfo);
}

When you publish the app you will see the following screen. Click the Trust button and afterwards you will see your brand new site provisioned under the parent you selected.

by Edge Pereira