james.
You are correct that the centre hole is the ski hatch. The other holes were cut to take a little weight out. It's as much as we were comfy with doing without removing too much structural rigidity.
I have been to visit the car again today.
The custom cage is an absolute nightmare. I would suggest that at least 50% of the bars were wrong and need modification. Some were stupidly incorrect and there is no way on gods earth they will fit. Pen has been put to paper and loads of head scratching to get over problems and it is just at the point where welding can begin. This has taken AGES though. Once it in will be a msterpiece but only because of the skill of the guy doing the work for me.
This lot still has to be put in place, along with another half a dozen pieces led on the floor at the moment
Where the 'B' pillars are thicker on a 4-door car they had to be modified to allow the door bars to pass. This was done by cutting and chiselling them out, making plates to cover them, spot welding them in place, then fully welding after. This is very time consuming.

Door bar now clears
The next step is to go through the front bulk head to the suspension legs. This isn't easy as there are several layers of steel to be cut through all at an angle. This also means the ECU have to be moved. The heater has gone to give space for the ECU. The jury is still out on how hard it will be to do the front legs against the end benefits.
Next up is to remove the door cards, cut away the inner skins and plate them. New fillets also need to be made to attach the cage to the car. The ones supplied were of such thin guage they were close to useless.
The suspension has arrived from Germany. It's a set which is specifically sprung for the Nordschleife, which is good as that's where it will live.
The heated front windscreen should arrive soon.
After a couple of mods to the dash that will be off to be flocked.
The car will be going to the painters to be coated inside and out in the non too distant future........
Another update to follow.
Gary