Have a look at the Unopiù catalogue:

http://www.unopiu.com/structures-pergolas-and-gazebos/1068/102/

and this item in particular:

http://www.unopiu.com/esdra/782/116/

But you can look at the Arles and Dafne models as well. I think that this is what you are looking for. The cover is made of polycarbonate (not plastic) as glass is no longer used for safety reasons.

Unopiù has products with an excellent quality. Prices are high, but you pay for quality. I think that the nearest shop for you would be the one near Florence,: 

http://www.unopiu.com/espositoreDettaglio.plp?idContent=63866&idNazione=127

If you go there, have also a look at what Leroy Merlin at the I Gigli shopping Centre can offer. I saw them in France, but I cannot find them in their Italian catalogue.

Good luck!

 We could make you a similar one. www.ironworkmarche.com

Not sure that qualifies as a porch  Jan...

I think it's lovely, but is this sort of added structure allowed on the outside of a home in Tuscany?

The reason I ask is because my in-laws purchased a home with something similar (added by the previous owner) and were forced to remove it when the home was inspected because it wasn't orginal.

A friend applied for planning permission to add a small, traditional style portico (brick columns, tiled roof) over her front door and was denied because any changes to the facade were not allowed.

A planning permission is always required. You must contact your Comune before undertaking any addition or renovation. Go to see them first and check what they may or may not allow. It would largely depend on the Comune and the particular building. Some areas have lots of restrictions. See this very useful old thread:

http://www.italymag.co.uk/community/post/listed-building-status