Roof insulation

Perhaps it is a good idea to visit new and expensive construction sites and talk to insulation workers or an architect regarding this.
I've seen that blue foam sheets about 3 cm thick are applied on the walls on the outside and then gray coat is applied prior to stucco.

I know that foam can be sprayed on the inside of the ceiling. But do you want to breath out-gassing polyurethane in the heat of summer?

The best "green" and not expensive solution so far that I can suggest for Maltese houses is retractable canopy roof made of fabric. It can be removed during the time when you actually want your roof to get warm from the sun. You advise you  to consult an architect for this. There can be very attractive designs done depending on the style of your house.  Put in your browser: "retractable canopy roof covers" and see images.

One more suggestion for your roof.
Have you noticed that many houses in Malta have black moldy walls? It is an eyesore. There is a way to prevent it from happening. Walk around and see that there is no mold  growth e.g. under extended window sills. I've seen a stone fence and some flat roofs which are covered with the roof tiles at the top around the whole perimeter. It is the same concept and protects from mold. It cost a little more upfront, but reduces spending on an expensive procedure to sand off the mold periodically off your house.

I've seen that sometimes they paint over the mold. Bad idea. Because mold will grow under the new layer and the new layer of paint will start pilling off.