We have a fireplace that we have never used, and that the former owners of the house rarely used. It opens into both the living room and the dining room, and the draft reportedly would reach hurricane intensity. After some years, we decided to turn it into a plant-arium, with potted plants and grow lights.
One of our criteria was that it should be relatively easy to revert back to a fireplace, should some future owner be that adventuresome. We thought about painting the whole thing white, but couldn't find a fireplace paint in anything other than black, and felt that regular paints would be a health and safety hazard if you built a fire on them. So everything had to be removable.
Here's how we did it.
Step 1: Parts List 1
What we are going to do is mount some boards up at the top of the fireplace, and put grow lights on them. So we start out with four boards. I used 3/4", because they don't have to carry much of a load, but I don't want them to sag. You probably don't want to use plywood here. Two of the boards are 4" wide, just wide enough to hold the lights. The other two are 8" wide, because they have to extend the width of the bricks. The length of the wide boards should fit the width of your fireplace opening.
Step 2: Parts List 2
Here's your put-it-together stuff: drill, saw, screwdrivers (both + and -). Wooden dowels, if you want to peg the joints, otherwise angle plates (not shown). Shelf brackets (4), as decorative as you like. Brick/concrete screws to hold the shelf brackets. Fluorescent grow lights (4). Wooden blocks to mount the grow lights on, because we want them on their side, sticking out over the edge of the board (for maximum light). White paint for the underside of the boards. Not shown: light timer, extension cord, power bar, stick-on floor tiles and stick on mirror tiles.