I've been reading about owning land in Thailand and about the 30 year lease that's popular.

What happens at the end of the lease? Does the house get sold back if you build one on the land? Or can you try to move it to a new piece of land or extend the lease? If you were at the end of the lease, could you just bulldoze it so no one else got it for free?

My understanding is that if it isn't spelled out explicitly in the contract any improvements revert to the owner.

There are of course some styles of housing, including traditional Thai wooden houses that can easily be disassembled and moved, modern pre-fab modular units, some people build with ISO shipping containers, haven't see wheeled trailer/caravan style homes here, but all of these could easily moved as well.

You should certainly have all this spelled out explicitly in the contract.

From a practical POV, keep in mind if the landlord decides she wants to re-occupy the land, there are many ways to get you out legal or not so personally I wouldn't pre-pay for the whole term unless I had a high-trust personal relationship with the owner.

And wouldn't spend so much money that it would actually affect my financial security if I had to walk away, which is IMO a universal rule for any so-called "investment" in Thailand.