Lilies: Dedicated lily bed... how to construct?, 1 by cinemike

cinemike wrote:
Hi,
I garden on a French limestone hilltop. There isn't much depth of soil.
I am a bit of a seed fanatic and I grow oodles of plants from seed. For the last couple of summers I have been raising quite a lot of lilies from seed... loads of L. regale and some L. henryi and L. philippinense and a few more.
I have a large (300 sq m) unpaved courtyard in full sun that I currently use to grow weeds. ;O)
I was thinking of making a large (maybe 4m diameter) raised bed in the courtyard to plant my lilies, thinking that I could dig down the same amount as I built above ground.
Two questions... does this sound like a good idea?
What total depth of soil should I aim for?

Other question.... any other lilies that can be grown from seed that I should try to grow to complement those mentioned???