A Laser Leveler on a tripod was used (the type used in construction work), to mark a line along the wall so it will be level with the old layouts shelf brackets. This device worked very well. I didn't want to use the room floor bacause our house was built in the 1930's, so the room is not exactly level from any point.
The metal shelf brackets were the larges that I could find at the hardware store measuring 11"x 13 ", then modified with two holes in the center of the 11" long rib for 3 inch long deck screws to go into every stud along the wall. I screwed a 1"x 2" x 18 1/4" wood to the longer end of each bracket to act as a pad for the 5 foot layout sections to sit on. Leftover 1"x 2" from the module frame construction were cut to 4 inch long blocks and screwed to the the top of the long wood pads an inch away from the wall. These keep the layout from sliding forward as the modules 1"x 2" back part of the frame locks behind the blocks along the wall.
These new modules were built to be 18 inches wide because of having more tracks, but two will be 5 feet long and the end module will be only 3 feet long. Modules that I have built with two inch wide frame have worked well, they are strong enough to be used as a book shelf or store concrete blocks on, that more than plenty for the model trains to run on.
As I have mentioned in the main web layout page, I'm not much of a wood worker and I don't have a garage full of wood working power tools. I own one crosscut molding saw and a cheep jigsaw. So this method of layout building is directed for those like me that are challenged at woodworking.
I purchased 1"x 12" pine from the local hardware store, trying to find clear board without knots is impossible, but found one with just a few. I asked a friend who has all those wood working power tools if he could rip it into 2 inch wide lengths. I began putting the module frames together that measure 18"wide x 5 feet long. Later the 1/2" plywood will be laid on top.
I didn't put any cross pieces into the 5 foot long modules yet, I still need to figure where my track turnouts will go. Nothing worse than having the turnout switch point over a cross piece. Because the turnouts will be operated from under the layout, so the cross pieces will go in later after the plywood top is attached and the turnouts located.