I'm assuming you're talking about something similar to a shelf attached to the wall. It's not difficult at all, just a cleat/brackets to hold it in place. One easy and relatively inexpensive way to go about it is to buy a section of countertop from the local home center. There are well over 500 different patterns of high pressure laminate (aka Formica) available.

Buy a smaller table with a leaf in in that you like, cut it in half and screw half to the wall.

Just a place to perch and snack - easy. it's really a "floating shelf".

Terrific ideas! Thank you all!