After some research I determined that while you could get a outer cover for an MGB there were none that I could find for a Dolomite. So I bought some outer material and some headlining material and went ahead to have ago on my own. It didn't take long to get the roof out - just lift out the runners (3 off each side) by canting the sliding bits over at an angle and drill out/sheer off the four fixing screws along the back (all rusted solid).
That was the easy bit.
Once I started pulling it all to bits it was obvious that the front a back steel plates were badly rusted all round the edges and unusable - in fact I was worried that they wasn't enough metal left at the ends to make a template. By looking at the top covering, marks left on the roof of the car I averaged out the outline and produced two new plates! it took a few hours to bend and shape them to the correct gentle curves to match the roof using a combination of an English Wheel and a shrinker/stretcher. I also had to remake/repair a couple of retaining bars spot welded to the original metal work.
Next was remaking the headlining. I obtained a length of the correct material. Using the old one as kind of template I stitched in the reinforcing tapes along the edges and the fabric "tubes" which the reinforcing hoops slip through. I also stitched in the rope beading on the back edge that secures the lining to the rear metal work. It was all a little bit of guess work as the original material had stretched over the years so I was never sure of the exact correct size.
The top/outside "cover" was next. What a nightmare. The material was quite thick and heavy and the sewing machine didn't like it one bit! The original was Heat sealed or welded together along the two outer edges. I had a go on a small section of the new material but it wasn't going to happen so sewing was the only option. The seam is needed to secure a webbing strip along each edge. I got there eventually and it does look quite neat.
Next stage was to put it all back together. Very fiddly and has to be done in the right order as once the top cover is stuck onto the two metal end parts you can't get to some of the other bits. I used Evostick 528 impact adhesive to stick the edges of the material to the metal work. Time will tell if it will last. I had several trial fits along the way to make sure I had the length correct so that the material (both head lining and the top cover) pulled taut when the roof was closed.
As you can see the end result looks OK. It still needs a few tweeks to tighten the lining up I the back corners.
I normally encourage people to have a go but I think this has been one of the most challenging jobs I have done on a car, requiring all the skills I have learnt over the years plus a few more. (metal bashing and shaping,English Wheel, Shrinking, stretching, turning (threaded inserts for the back edge), sewing, fabric stretching and shaping, hemming, bonding, sealing) and I would say it is not for the faint hearted. If someone produced the correct cutout fabric as per the MGB it would be easier but there would still be the issue of the rotted metal work - which has to be pretty spot on otherwise the front will not close down snugly.
That's the bravest repair job I've seen in a damn long time. And what a result! Chapeau sir, chapeau. 
I would not be brave enough to tackle that! 
