Have a look at the Elica Pro Anglo
pro kitchen ones are dearer than you might think
www.nisbets.co.uk/parry-titan-extraction-canopy-2400mm/gh194
I knew a company that made them for commercial kitchens, they seemed to measure up and make to order from galvanised or stainless steel sheet folded and welded.
The extractor duct is a large rolled tube, not the small flexible or plastic pipe used in domestic kitchens. However you could make up your duct from 150mm plastic pipe with elbows and angles, as used for sewage. You could spray it silver for an industrial look. The flexible plastic domestic hoses are not much good.
Used catering equipment is always on the market, greatly reduced from the new price, because most new restaurants seem to go bust. I'd suggest stainless steel because it is so easy to keep clean, and doesn't rust. If you do take the second-hand route you could blast is with a pressure washer and detergent.
If you can get hold of a canopy and ducting, there are extraction suction units that can go on the outside of the building (I believe this is because big ones are noisy)
A domestic canopy might have an extract rate in the region of 250 cu.m/hr at high speed, as a guide. You can get extraction units to build into your own canopy from makers like Elica who I think are good, (their website is awful but they will send you their glossy brochure if you ask). Look for the dimensioned drawings on the web pages.