Create SLN Programatically.

// Add Ref to EnvDTE80.dll
// Warning : Close All VS instance before running :)

public string BuildSolution()
{
    StringBuilder status = new StringBuilder("Projets non traités :");
    status.AppendLine();
    try
    {
        EnvDTE80.DTE2 dte2;
        dte2 = (EnvDTE80.DTE2)System.Runtime.InteropServices.Marshal.GetActiveObject("VisualStudio.DTE.11.0");
        dte2.Solution.Create(@"D:\Temp\", "AllSLProjects");
        foreach (string projectFile in this.allProj)
        {
            try
            {
                dte2.Solution.AddFromFile(projectFile, false);
            }
            catch (Exception ex )
            {
                status.AppendFormat("{0} : {1}{2}", projectFile, ex, Environment.NewLine);
            }
        }

        dte2.Solution.SaveAs("AllSLProjects.sln");
        dte2.Quit();
    }
    catch (Exception e)
    {
        Debug.WriteLine(e.ToString());
    }

    return status.ToString();
}