A friend and his wife visited the nursery recently and commented on the trays I use to sow seeds and the divisions from twin-scaled bulbs. They are actually meant to hold pots called bands, but when I bought them for that purpose, as soon as I saw them I knew I had found the ideal flat for growing bulbs. They measure 15.75" (40cm) x 15.75" (40cm) x 6" (15.2cm). I had long dreamed of a pot with a mesh bottom to allow even, rapid drainage that bulbs need. I had, in the past, grown some seedlings in large round pots that were about 12" deep, but I had to drill extra holes in the bottom, and still the medium would be much wetter in the center than around the edges of the pots, and I often found I lost the seedlings in the center of the pot. I have to line the flats with something so that the medium doesn't fall through, and I have used landscape fabric, but I am currently using row cover fabric cut into squares. Any kind of mesh will work as long as it lets water drain evenly and rapidly. 
I sow fairly large quantities of seed, so I will sow directly into the flats. I have on occasion put dividers in the flats and sown two different kinds of seeds that need the same conditions. The seedling bulbs are left in the flats for about two years then transplanted into whatever size pot they like. Some bulbs, like Rhodophiala, absolutely require a deep pot, while others can stay in the flats if they are smaller bulbs and don't need the root room a deep pot provides. Almost all my Oxalis are grown in these flats.
Here are some flats of Amaryllid seedlings covered with shade cloth.
www.telosrarebulbs.com