I'm not sure why the prototype Bulldog has a canvas roof not unlike a convertable sports car, but it does and therefore so my model must have one too. It's quite handy as in The Book, I wrote a cab in to the story.
Anyway, I don't think the roof is removable, at least not easily. When I started, I didn't know how I was going to make it. Since you can see both inside and out, the material had to be thin. Proper modellers would build a prototypical structure and drape gossamer thick cloth over it. More practical people would make a master and vacuum form plastic over this.
I'm not clever enough for the first and don't have the tools or equipment for the second.
Instead, I made the basic shape out of 0.75mm thick plastic sheet. In the top there is a single microstrip rib, sanded to shape. The rest of the roof is three coats of Deluxe Materials filler sanded to shape. While the sanding stick was out, I rounded off every corner and thinned down the edges slightly.
The result is OK. Yes, it's far thicker than it should be but then I doubt the real material is much more than 3mm thick. The only place it's really obvious is in the roof and you can't see under that can you?