Is this range hood for a residential kitchen? Is so then why do you need a 700 - 1000 CFM range hood? If you want quiet operation and the air flow you paid for then you will need to install a 10 - 12 inch vent pipe up through the roof. I am not sure if you can find an off the shelf vent cap of that size. You may need to have it fabricated if you intend in putting in a range hood of that size.

Have you looked into the the make air requirements for a 700 - 1000 CFM hood? That should be your first priority if you have other gas appliances in the house.

If one wants full capture and containment, the dual-purpose of a cooking hood, then two key parameters have to be achieved. The hood has to overlap the cooktop sufficiently to capture the rising and expanding cooking plumes from the burners/hobs, and the air flow rate has to be high enough to assure that the captured plumes are pulled through the filter and not allowed to reflect back into the kitchen. This requires sufficient air velocity at the hood canopy entry aperture. Adequate depends on what is being cooked, the temperature it is at, and whether the plume is augmented by gas flame combustion products.

I suggest 90 CFM/sq. ft. of entry aperture (achieving 90 ft/min). This value times the entry aperture in square feet yields the required full power volumetric air flow rate (CFM). To achieve this CFM in the presence of pressure losses in the hood baffles/filter, duct, hood to duct transition, duct to roof cap transition, and significantly the make-up air (MUA) differential pressure achieved, requires a blower with a zero static pressure rating higher than the required flow rate. A factor of 1.5 may be a good starting point for analysis.

It is easy to get to a rated 700 - 1000 CFM blower depending on cooktop size, although without more information we cannot determine the OP's actual need.

In my view, the hood should be blowerless, and the blower should be on the roof. Typical down roof blowers such as Broan, Wolf, and Abbaka sell are one useful style. They have automatic dampers that open when active.

The alternative is an appropriately sized up-blast blower such as routinely seen on restaurant roofs (only smaller) that has its own advantages and disadvantages (mainly heightened visibility).

If enough duct length exists and space around it is available, a silencer can keep the blower noise down to conversational level.

The OP should review the myriad hood threads on this forum, along with MUA threads, to gain an appreciation of the factors involved in adequate kitchen ventilation. For background, there are commercial reports that may be found on the Internet, such as from the California Air Resources Board. For a good summary, the first dozen or so pages of the Greenheck guide may be read.

http://www.greenheck.com/media/pdf/otherinfo/KVSApplDesign_catalog.pdf

Why are you even dealing with parts from a hood maker? You should be dealing with a HVAC supply house where you can find real ducting needs. Including all manner of roof caps and dampers.

A tour of Fantech's web site, as well as Broan's should expand your appreciation for what is available.

When you say 'roof vent' I assume you are looking for a roof mounted blower and not simply a roof vent (or roof jack)?

There are hundreds or thousands of roof vents available and most HVAC contractors can easily make them. Have you considered an inline blower (Fantech) + a simple roof vent?

You might also try https://www.accurex.com

"What do I need to buy as an actual range hood with an inline blower? Do they sell range hoods without blowers?"

Yes. You'll get better performance and less noise with an inline or external blower.

More Here: https://www.gardenweb.com/discussions/5161173/hood-faq

For a vent/cap/jack talk to your builder's HVAC folks. There are a few considerations depending on where it will go, angles, static pressure, etc.