Well you can start by making or buying a form to make the vents. I do know for a fact that Robby @ RLD Hobbies just got three different size forms to build the vents for trestle. From Small to Large. I used them several times, because his collection was sold after he passed away. They are very nice forms. Use a form get your wood and use glue and a brad nailer !want to build a G gauge trestle not big where do i start ?