A laboratory is a fundamental tool for every Magus in Ars Magica. As such there are variations and rules in abundance for how to detail and personalise a lab (Covenants source book, p 106). Just to be slightly odd I thought detailing a few aspects of a floating lab might be interesting. Typically to find a structure for a lab isn’t difficult but finding something which is suitable as a portable and floating lab is harder, it’s either constructed purposefully by understanding mundane craftsman or conjured.
If constructed the sourcing becomes a challenge only in resolving how the building is designed for flight. The Magus comes to acquire the stonemasons, labourers, and materials of the build in context of their covenant resources.
If conjured the sourcing probably requires a bespoke spell for the shape and size required, so it adds seasons of work or vis to be spent if another Magus is supplying the solution. It does however grant the owner exacting design choices and options which would be very difficult for mundane craftsmen to complete.
Rather than a conjured room or tower which is then enchanted, I suggest taking a lead from the floating castle in Legends of Hermes (p.121), by using a massive sheet of stone as the base with a Rego Terram effect, say one pace thick by 30 paces across. That requires a constant lesser enchantment as ReTe28. This allows the stone sheet to move at the speed of a running horse. Then if it is commanded in the same way as The Flying Castle of Thomae then another constant lesser device of CrIg9 is needed to send the colored light as control commands.
A 30 pace wide disk is far more than large enough for a single lab and likely could hold a small tower, or many ancillary buildings too. The disk itself will have the same abilities and failings as listed for the flying castle. It’s plausible to have the disc far smaller than 30 x 1 paces to make a smaller block, especially if the next task is adding a multi-story building. It could be about 15 paces wide and still hold a huge lab, and reducing the blocks diameter makes it easier to fit into a lab for enchantment (note though the Ars rules allow for an outdoor lab, so it’s plausible to create a place to enchant this easily). Perhaps a block roughly 15×2 paces is better as it makes for an incredibly sturdy base.