If he's looking at new builds in higher end neighbourhoods, I'd expect he's looking more at retrofitting existing shells, likely during or shortly after the initial build process.
Rather than having specific packages for say the weekend mechanic, the detailer, the wood worker, etc, the real money would be in educating on and sourcing premium quality products and offering design, project management and basic installing services for those products. As far as I've seen on the forum here, the biggest problems people face have to do with deliveries being just dropped off in the driveway, damage done to products on their way to the site, lack of knowledge of the options that are available, and general frustration due to contractors, delaying projects, under delivering or not delivering at all.
Educate the client on the best products for their needs, design the layout, subcontract/manage the delivery and installation, and get out. To really nail it in the market he's looking to access, I'd suggest establishing relationships with premium quality lighting/sound/AV/electrical installers, flooring distributors/installers, cabinet makers/distributors, etc. for the big ticket items, and then source the rest of the more nitpicky stuff himself to install, ie air systems and . It would be a whole lot more project management and less labour work, which he may not be up for, but I think the major value in terms of a turn key solution is the ability to manage a project in such a way to minimize pain and frustration by ensuring your deliverables are met on time, on budget at exceeding expectations.
It's really about pulling all of the best products and services together and ensuring that the design, timeline, and finished product all meet the client's needs to the point that they don't really have to worry or think about the project once the design phase is done. That's where the value is to the consumer.
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