Prior to purchasing my house, one of my many apartments was a basement level. This meant that while nice, it was somewhat dark, though it had windows. The nice thing was that since it was in the basement, the living room area had a shelf that followed the outer walls. I thought initially it was odd, but once I placed my sofa up against it, I realized it provided a nice decorative shelf to giving me the chance to brighten things up through decor.
Well, the darndest thing happened. I learned to love the ability to decorate in back of the sofa, and found myself really missing that shelf in my next apartment. The living area was too small to support a full sofa table, and I didn't have the money to spend, so I DIY'd it up! I have done the same thing for all subsequent moves, and haven't stopped loving the results.
I should say that this only works when you are putting a sofa against a wall. If your sofa is in the center of the room, you should get an actual sofa table. The "sofa table" you are making is really a shelf. It doesn't matter what the color of shelf or brackets that you use because you won't see them, so purchase whatever is cheaper.
Decide how wide you want the sofa table to be and then purchase your shelving accordingly. To save even more money you could just buy "1 x width desired" boards. For example, "1 x 6" or "1 x 8." You also need two shelving brackets for each board. You can get these for about $2 at Lowes.
Next, mark where the top of the sofa (not the cushions, the actual sofa) hits the wall. That is where you want your shelf to be.
Mount your shelf there and back the sofa up so that the board sits just at the top of the sofa.
That's it! You have a faux sofa table. I love to put pictures, flowers, and seasonal decor on mine. I usually have some kind of garland so you really never see the shelf itself. You can adjust how far out you want the couch to sit in relation to the shelf.
This has been as fun to decorate as any mantle and has really given me a great way to cozy up the living room! Do you have a sofa table?