Also, found this resource on Amazon.
Trays 3 and 4 are 6 rows wide.
I built this rack to hold the trays. Each level can hold 4 trays. The rack is +/- 5 feet thinking that future expansion will add trays toward the bottom. The level offsets are to allow sun to reach the level, however, if I understand, during germination sunlight is not a critical factor. This shows the 4 trays domed for the initial stages of see germination.