For the ready-made A frames that are sitting around: pick a corner and remove the floor tile if there is one. Take out the roof panel right above it and part of the front (or back) wall, leaving enough at ground level to keep unwanted guests outside. Put in a new roof panel facing the wall that you just trimmed so that the smoke is directed outside. It doesn't look pretty but it works.

Or, put the fire right outside, up against the building, with its own protective roof and half walls.

More or less the simple rules are to leave one full square of venting to the outside, and a roof that directly covers the fire. Avoid leaving a full square of venting space inside. Short walls or beams to keep yourself from stepping in it are recommended.