Out of curiosity, what "amenities" come with the shell and/or what options have your ordered(is there an electrical system, etc...)? What vehicle will you be pairing it with?
The FWC flatbed starts at $29k but they don't offer a shell option so I see how Bison is filling in a gap there, was there another appeal over getting a FWC? You may save some money building it how you like, but you now also have to be the designer, engineer and technician of a one of a kind camper.
My advice is keep weight toward the front, make storage accessible and think about how and where you will use it. Make a list of things qualities you care about (privacy, comfort, style, indoor vs. outdoor space, hauling recreational gear like bikes or kayaks, etc...), then how and where you plan to use it (weekends, multi-week or drive around the world....summer, winter) then list what you want to include (fridge, stove, sink, heater, hot water, shower, etc...) then decide how to implement each one based on the qualities you want from the camper and the intended use cases...write it all down....probably on spreadsheets and get ready for this to consume your life and for you to wonder if you shoulda paid the extra ~$9k to FWC for an already built out camper....BUT, keep your eye on the prize, you'll be left with a unique, custom camper that meets your needs better than any "factory" camper could.
I have a standard galley style FWC and many people really prefer the dinette option. I think I would like it too, but with the galley we have just enough room for the dogs to hang out inside and then enough room for them to sleep downstairs at night. This flat out wouldn't work with a front or side dinette unfortunately (the dogs are not small).