Sounds plausible. Then it would be more like underfloor heating in the screed. I thought that in the simplest case, you use a kind of "hollow paving stones" through which the corresponding pipes/conduits are laid. Maybe I'll give it more thought once the outdoor sauna is standing.
That also works electrically under any covering. I'll send you a PM.
But the craftsman has to cooperate as well. Given the workload, any craftsman in our region (BW extended Stuttgart suburb) would laugh at you. (Based on official offers) Here you already pay four-figure amounts if you want a plan from the landscape gardener.o_O
He cannot receive it. Has only 10 posts. But I don't dare to advertise here. Already have 2 warnings. But you can google "Heizung Garageneinfahrt" then it comes up as the first result.