There are several suppliers of good tops. As I understand what has been discussed, what is needed is evaluation by buyers of different manufacturers offerings.
The Giulietta top frames are distinctly different from Giulia. From what I have observed, this was not so much a 750 /101 Giulietta 1300 change, except for length to match the SWB chassis, but a difference in the front bow height, and mechanism folding (with and without the rear locking handles and red lifting handles). This change seems to have been made with transition from the 1300 to 1600 engines. The 1600 cars feature the later mechanism with locking handles, (black) and lifting handles (red) and a low front top bow. Therefore, it seems there are three basic tops, 750 SWB, 101, 1300 and transition LWB cars, and late 101, 1600 low top bow.
Original tops were canvas material, not terribly durable, but nicely attractive. These were made up for PF. I had a NOS PF canvas top in a PF box for years for my 65 1600 Veloce, and when my original top material finally was failing, I installed the OEM replacement. It was not easy to fit, and took my efforts plus an upholstery shop, but came out beautifully. This may have been because it sat in plastic in a box for 40 years!
I have seen some of the Robbins tops and they too are beautiful, and seem to fit (the later) cars well. I've only seen the low top bow 1600 version. The thread count of the material is way off the original, the canvas having a much higher thread count. I did save my original top as a pattern, but fear that is so dry rotted it may fall to pieces if used for a pattern.