Decks, Patios, Porches and Docks - Grille Box

Looking for plans for a Grille box that I can build and add-on to my deck so I do not take up any of the space inside the rails.

Welcome to the forums! Although it is always better to do this as you build the deck, it can be done as an afterthought. Basically, all you do is build another "deck" the size you want using band boards, joists and decking(in the opposite direction for eye appeal), and vertical support on the outside extremities. You will have to remove and extend your balustrade to match what you have, and may have to add newel posts if your opening is narrower than the existing ones.