I needed another shelf 37"H x 45"L to fit at the end of my other shelf. A few weeks ago I went to one of those large hardware stores to get lumber to build a shelf. I bought 8- 1"x4" & 1- 4' x 8' luan , had the store cut the 1x's in 4' lgths, and luan into 4' x 4'. By cutting the 1x's and luan, made it easier to handle and work with.
Dado'd the side of the 1x's and 2 furring strips (furring strips allow more strength for shelves and secure to the wall) , ripped two notches the lgth of the shelves for train car wheels to fit in. Glued and screwed it all together, painted it white, hung it and put some engines on it.