Say someone is selling a building with chanote, but I wish to have the building, which I can own 100% legally, in my name and the land, which I cannot own, owned by a Thai company. In simple practical terms, what is the process and what do the parties end up with ?

Does the building have to pay rent to the land owner ? How does it all work ?

Well, actually the buildings do not have title documents such as chanote, the land has.

In your case are you talking about an existing building or a plot of land on which you want to build a house? The procedures are different.

acceptable proof that you own the building is the building permit in your name and that the payments for the construction were made by you. whether you pay rent or not is a different animal and depends on the individual situation.

As the situation envisaged is a resale the OP as new owner can't have the building permit in their own name or 'their own' new thai company's name.

A sale and purchase agreement will be required for the building backed up by a lease or other right to use the land.

There should of course be appropriate due dilligence and the contracts should apprpriately deal with all potential eventualities.

Payment for the use of the land would be expected by the land office (whether it actually leaves the OP's right pocket is another matter) and there will be tax issues for the landowner (essentially the OP's left pocket?).

There are of course multiple issues here concerning land ownership, control of company and rights of use over land.

Hopefully this is only the first (simplistic as requested) step in the OP's consideration of the issues.

Regardless of the relative monetary values that might be involved the penalties for illegal structures should not be disounted merely on previous selective enforcement.