Use 1 1/4" nails and glue to attach the trim pieces to the 1x12s. Do this on both 1x12 boards @ 46 5/8" long. Make sure you have drilled your pocket holes (see step 2) on the 1x12s first.

Drill pocket holes along the sides of the 1x12s set for 3/4" stock. Attach the legs with glue and 1 1/4" pocket hole screws. Tops are flush. This is the back view, the front view has the trim boards.

Now create your top shelf as shown here. Use pocket holes set for 3/4" stock along the sides and glue to attach the 2x2 trim to the top shelf 1x12.

Now attach the top shelf to the two ends as shown above. The easiest method is to use pocket hole screws from the top, as the top will be hidden.

On the back side of the desk system, we need to add some boards to support the storage space and to fill in the back so we can add plywood. Attach the 2x2s - you can use 2" finish nails and glue, 2 1/2" countersunk screws or pocket holes.

One more support added in the same method as step 6.

Now you will want to join these boards to the 2x2 back frame with pocket holes on the inside/underside set for 3/4" stock. Use glue and 1 1/4" pocket hole screws.

Attach the plywood to the back with 1 1/4" finish nails and glue.

Drawers should always be made to fit the opening, so you get a nice tight fit. I did give measurements that work in a perfect world above. Build the drawer box out of 1x3s, to a total overall size 1" narrower than the opening, and leaving room for the drawer face (cut the sides of the drawers at 10" long). Use the drawer slides to attach the drawer in place without the face. Remember that the face is inset, so the drawer box will need to sit in 3/4". Then cut your drawer faces to fit and use 1 1/4" finish nails and glue to attach the drawer faces to the drawer boxes, keeping an even gap around the drawer faces. Attach hardware.