For an outdoor fireplace, “the most cost-effective option would be a prefab insert,” Maestri says. As with anything, you can go high or low when it comes to outdoor fireplace ideas. Movable lanterns or subtle uplighting around the fireplace is usually best.”How do you make outdoor fireplace seating comfortable? When you buy or build quality, you can expect your outdoor fireplace to look hot (pun intended) for decades and beyond. “If you build an outdoor fireplace with a masonry firebox, and proper flue system, it should last forever,” Hefner says.