Using an old coach or shipping container for business

A few years ago, I started a thread on the possibility of using either an old coach or a shipping container as office, and it started a really helpful discussion. I have just spent the last half hour search for it among my old posts and can't find it anywhere, so forgive me. Here I go again.

I am once again returning to the idea of buying and using an old coach, a shipping container, an old railway coach, or a wooden 'cabin' as an office and small social space. It would be located on disused land on the outskirts of the city.

I seem to remember people on here saying 'don't do it' for a number of reasons, but it was so long ago that I can't remember what they were.

So, I am wondering once what the hazards of the idea might be. Of the four possibilities I have mentioned, which would be the best (or least bad) and why? I mean, if I can get an old double-decker for between five and ten thousand pounds, is there a reason it would not work (setting aside questions about planning/utilities/etc.)?