The Brew Cabin

A question for you experts:
I wish to lay your stone flags inside my barn conversion. The screed contains under floor heating pipes. Are there any special consideration for the inside nature or the UFH. Laid on mortar, or special adhesive? Lean mix or strong, etc?

Lay on a bed of 6:1 mortar, and allow for movement joints on any span of more than 6m.

And what's this "your stone flags"? I don't have any stone flags; at least, not any I'm wanting to sell!