There are a few around marketed as specifically for bell tents, but do I need one that says it's specially for bells? (for instance, I'm sure I've seen one that attaches to the spike at the top of the A frame, but surely that's just an eyelet in the middle of one side of the tarp? 
)
There's the one sold by Bell Tent co and Obelink (obelink is selling it for 55 euros - I can't work out if it's one of the things they won't ship to the UK) but I'm not sure how large it is compared with others. There's this pretty thing, but £225?! And the one from Tortuga Tents is pretty expensive too, and only comes with one pole. But I just don't know what is reasonable for a cotton canvas tarp.
Ideally, we'd like to be able to have a pitched 'roof' extending from the entrance, for boots, outdoor storage, and so on, but it'd be useful to use the tarp alone in various configurations for picnics, etc.
Glampy sites and companies aside, does anyone else make cotton canvas tarps for camping, or are they likely to be all synthetic now? Could I even make my own, or would I need an industrial sewing machine for working with heavy fabric?
Thanks for any pointers!