Skylight, flat roof insulation

Wondered if anyone had recommendations about having a skylight fitted.  It is on the first floor landing in a space where there used to be a skylight but has since been roofed over.  We would also want to have insulation on the flat roof around it at the same time.  Not sure whether to approach roofers, insulators or window fitters so if you've done anything like this recently would appreciate a heads up.