I saw this stunning fireplace "Cover-Up" in This Old House and felt it was a must share.  The simplicity of putting this cover up together is great for those first timers!  In the summer my fireplace just lets out the air conditioning and I basically leave some logs in it or sweep it out and place a few potted plants in the hearth.  All this project consists of is MDF board- the thin ply- cut to the opening size, primer, paint, velcro strips, and embellishments.  Measure and have your local home/hardware center make basically two cuts.  They should give you two free ones and after that it's in the $2 per cut range.  Lightly sand down the edges of the board, prime with Zinsser Primer, once fully cured, apply two coats of Rust-Oleum's Sand.  Lay out your wooden scrolls and embellisments, prime - allow to fully dry and apply two coats of Rust-Oleum's Antique White.  Both of these Rust-Oleum paints are available in spray, quart and 1/2 pint.  Once the MDF board is dry, lay out a design with the embellishments.  Apply the embellishments with Gorilla Glue.  On the reverse side peel & apply the velco strips in a few places and same on the fireplace - push your decorative cover over the opening and Whalah - a decorative and beautiful Fireplace Cover-Up.