I guess the biggest pit fall is that you really want them open to the sky for ventilation and effect. As for height of grate you want a little lower in the middle to keep all the sparks from flying everywhere, you will need to clean it out no matter what you do so just get prepared to do that. The ashes are great for the garden . A metal liner is nice for ease of scooping out ashes as for rain , I would not bother with a cover, probably more hassle than it is worth.