private static bool CheckSPSite(string siteName) 
{
            using (SPSite site = new SPSite(siteName)) 
            { 
                using (SPWeb web = site.OpenWeb()) 
                {                     
                    if (!web.Exists) 
                    { 
                        return false; 
                    } 
                    else
                    { 
                        return true; 
                    } 
                } 
            } 
        }

I would recommend creating util Library where you can store all your helper methods and re-use in other projects.