I'm looking up the workshop rules in City & Guild as I'm pondering over a Verditius magi. I'd like to make use of the rules for Workshops which makes sense to me, as you would think a Verditius might care about making an excellent item as part of the enchantment. But there's a couple of things that bother me:
The craft level penalty for working in a magical aura seems unintuitive. Making it more difficult to craft an item in the lab, where you would think the workshop would be located;
The workshop Innovation and Raw Materials score being tied to the Labor Point system which looks extremely unproductive for a magi character.
Have you done this in your game? Do people assume it's the forge-companion that make the workshop improvements? Did I miss any rules about compatibility between hermetic labs and C&G workshops?
I take note that Verditius Magic enables them to manage things not even possible in a workshop. So if they spend a season on an item using Verditius Magic to open it, I put it at the limit of Excellent for their Craft score. Without this, vanilla Verditius Magic can fall behind Rego craft magic.
If they're not doing the Verditius Magic thing, then I hold them to workshop totals.
The C&G Workshops are mundane affairs, written for handling independent craftsmen.
The rules are written with no means to improve or maintain a workshop with magic. Any workshops build in a Covenant (including in a lab) can and often are at an advantage to ones in a purely mundane location. For one thing they can receive enchanted items which (based on SG decision) can provide an increase in Innovation. Finding and maintaining improvements in Raw Materials might be handled by the Covenant, ether by producing it internally or handling the purchasing, which would handle cost of them.
This is because most Covenants are effectively one large "company" which employs all of the Covenfolk and owns all of the facilities. If you are using the rules in Covenants, then the Covenant itself pays for the maintenance of any workshops. Generally integrating a mundane improvement in Innovation will require a Craftsman to spend labor points, since they are spending time setting up some new tool or process. However as stated above the Covenant is the entity that often handles ordering or producing supplies and raw materials. Individual shops can still handle the ordering of supplies themselves, though they will often have to ask the treasurer of the Covenant for the funds.
That is not to say that you can not include one in your lab. The Hermetic Shipyard in Hermetic Projects is actually built as a Lab and Workshop. It mentions using a Forge-companion as the mundane craftsman (p.56) and has a box detailing roughly how this would work (p.62). You can (and I suggest should) read through the whole chapter yourself, but the key point is that a Magus tracks their time differently from a Craftsman so having a mundane craftsman handle the Labor Points is by far the easiest way.