Hi and welcome to the forum. I’ve seen builds on Berlingo and Caddy vans. The Caddy has a very good reputation, but can be a touch pricy compared to other makes. I’d be tempted to have a trawl on the net and see what others have done. Of course, all depends on budget and your needs.
Good luck with your plan,
Theres lots of us here in Devon. I presume it's as a camper for one? space gets tight in a small van for more. I've looked at the Peugeot experts as a small camper that seems do-able for one. The Caddy's and berlingos do seem a little too small length wise for beds/ habitation areas.