A central fireplace is a great addition to any home, providing warmth and a focal point in any room. Here's a simple design for an indoor wall-mounted central fireplace:

Materials:
1. Fire-resistant wall board
2. Steel frame
3. Fire bricks
4. Glass doors
5. Chimney pipe
6. Heat-resistant paint

Design:
1. The fireplace will be wall-mounted, meaning it will be attached to the wall and will not touch the floor. This gives it a modern and sleek look.

2. The fireplace will be centrally located, making it the focal point of the room. It should be at a comfortable height for viewing and warming the room.

3. The fireplace will have a steel frame for durability and stability. The frame will be covered with fire-resistant wall board to protect the wall from heat and fire.

4. Inside the frame, fire bricks will be used to build the firebox. Fire bricks are specifically designed to withstand high temperatures.

5. The fireplace will have glass doors on both sides. This allows for viewing of the fire from both sides of the room and also helps to distribute heat evenly throughout the room.

6. A chimney pipe will be installed above the fireplace to vent smoke and gases safely out of the house.

7. The outside of the fireplace can be painted with heat-resistant paint in a color that matches the room's decor.

8. For safety, ensure that the wall-mounted fireplace is installed properly and securely. It should also be located away from flammable materials.

This design is simple yet elegant, and it can be customized to fit any room's decor. The wall-mounted central fireplace not only provides warmth but also adds a touch of style and elegance to the room.