In a small bathroom space is at a premium. Recently I replaced a vanity and counter-top that ran the length of a bath with a European-style, shallow-profile vanity. At that time, a new light fixture and a re-framed medicine chest were added.
While those improvements were needed, the reduction in counter and under-sink storage space were a problem. So, built-in shelves were next.
Finding the studs was the first step. A standard stud-finder worked like a charm and from there I could measure out the 16″ centers and start taking out the drywall within the selected space. (interior space between studs is normally 14.5″ unless you have an unpredictable old home or a nutty contractor built the wall)
Once the drywall was punched out using a flat-head screwdriver and a hammer (most efficient way I have found), a couple shelves of 3/4″ plywood were cut and inserted. Friction plus some wood glue made for a good tight and permanent fit.
I used some left-over 4 x4 stone tile ($5/sq ft) for the main part of the shelf tops and some smaller squared sheets ($10/sq ft) for shelf accents and the back of the shelves. After tan grout is worked into the cracks the shelf under sides and frame will be completed with poplar stained to match the mirror frame.