Wells Expeditions have posted two pages detailing custom units for two of the factions in their Arcane Legions fantasy game.
From their website:
The first two pages in our series of articles on custom units for beginners are now up.
These units are designed so they can be built using only a starter set and an infantry pack, cavalry pack, and booster bundle from a particular faction.
We do not have a page devoted to Roman units yet. These were left until last because at GENCON, the players who were interested in this topic were mostly playing Egyptian and Han. The Romans were too busy winning or something. In the meantime, we recommend this article on Gaul sorties.