maintenance page for VIP with different hosts point to different pools if available else redirect to http://$host/maintenance

Do you mean this irule ?

when HTTP_REQUEST {
     Check if the URI is /maintenance
    switch [HTTP::uri] {
        "/maintenance" {
             sets the timer to return client to host URL 
            set stime 10
             Send an HTTP 200 response with a Javascript meta-refresh pointing to the host using a refresh time
            HTTP::respond 200 content \
                " \
                Sorry! This site is down for maintenance." "Content-Type" "text/html" 
            return
        }
    }

     If the respective pool is down, redirect to the maintenance page else 
     send the request to the respective pool 
    if { [ active_members [LB::server pool] ] < 1 } { 
        log local0. $host 
        HTTP::redirect "/maintenance?uri=[HTTP::uri]" 
        return 
    }
}