In looking at my old wheel build notes from decades ago, the lengths available are tolerable, not optimal.
308's would be for 32 holes for SOME rims and 4x for a few 36 hole rims... Then you are stuck if you want to do a rear wheel where the drive side can easily need 1-2 mm shorter. I don't like over length spokes, no too short where the nipple is not fully engaged.

I worked with Robergel a lot, before DT were readily available. You did have to check the length, we worked from bags of 500, easy enough to do, but yes, an extra step. DT had better nipples, true length, we migrated to them as fast as we could starting in 1975. It was a box of them that I won in a race that started that cascade, 305's that I built with Tipo large flange hubs and Super Champion Pro rims, bulletproof. We did not order Wheelsmith, at the beginning Wheelsmith was promoting the building of wheels over selling spokes, that was competition essentially, plus you had to ship them hubs, or buy them from them and had to pay shipping back. All for that Wheelsmith serial number logo...