Got me confused.

Do I look at shape&material section for suitable focus and write it down to a spell so verditius mage can cast his spell, or do I open up 4th edition and see what kind of spell focus is meant for any given spell?

Shape & material section sounds better, cloak for invisibility etc. Gives some freedom.

Plus, verditius has been explained really really strange, the wording does not make it clear.

I'll check how it was defined in 4th edition.

So I guess shape & material table is good starting point.

But I still do not understand how to utilize the virtue.

Can I get it in plain english because it's a bit hebrew in the book.

Let me see if I can help out, I play a Verditius and had some of the same problems. First off your casting foci for Formulaic spells are personal, but using the form and effect table is a good idea if you're having issues deciding. I had a Verditius who specialized in toys, thus all of his foci were small and toy like, often a representation of the spell. It's whatever makes sense, in his case for example a Pilum of Fire was a small toy spear, and an Aegis of the Hearth used a full on diorama, complete with moving parts. My new Verditius uses tools associated with architecture, carpentry and masonry.

For how Verditius magic effects your lab work, it's like this. First off, if you have a relevant Craft that could apply with the item you're enchanting, you get to add your Craft score as a lab bonus. If you're creating a ring and had Craft: Jewelry that would apply, and if you had a specialty in rings it would apply also. Second, you can merge things together easier. An ordinary magus can enchant a gem and fix it to a staff, and the gem's effects would get the bonus for the staff (+4 to control things at a distance for example), but it would not get the material of the staff (wood for example) as a bonus. A Verditius can get them all though, the wood, the staff, and the gem. However, just like an ordinary magus, that bonus cannot be higher than their Magic Theory. Finally, by using Verditius Runes, they get to add their Philosophaie score to their lab total, again not in excess of their Magic Theory. This means that a Verditius can add up to his Magic Theory twice, almost no matter what he invents, and what shape and materials he invents. A regular magus creating a device that creates light, is going to want to enchant a Lamp most likely, if he wants the extra bonus. A Verditius could get that same bonus (assuming his Philosophaie score is high enough) and invent a light creating device out of anything pretty much. That's the main difference. They get to add their Craft score (possibly) and they get to add another bonus either from the shape and material or their Philosphaie score or both, up to the limit of their Magic Theory.

They have one other big benefit, if they use the Veditius Runes, they reduce the amount of Vim Vis needed to open the enchentment by their Craft score, down to a minimum of 1 pawn. That's a major benefit considering that you can only use as much Vis in a season as twice your Magic Theory.

This might be a stupid guestion, but I just want to make sure that I got it clear:

Does a Verditius magus add both Craft and Philosophiae, with each limited by the Magic Theory score, so that if a magus has MT 4, Craft 4 and Philo 4, he gets both Craft 4 AND Philo 4, for a total of +8?

Or..

Is the TOTAL of the bonus from Craft and Philo limited by MT score, so that the magus with 4 in everything would only get a +4 bonus?

craft addition is independent of and unrealted to the use of Philosophiae; instead the use of Philosophiae is combined with the additions from Shape & Material Bonus components, and the total of (S&M bonus + Philosophiae) is capped by MT.

Think of is as: to get a bonus, most magi are considerably constrained in to physical design of a device, struggling to find S&M bonuses to get up to their MT. The Verditius magus can use Philosophiae *instead* of SM& bonuses, and can make their device in any form they want.
More, once they can make it in any form they want, they are free to choose a device they can Craft themselves, and so enable their Craft skill addition.

(Consider the Woodcarver Verditius, who is comsidering a device normally made as a golden lamp - by replacing the S&M factors by Philos., he can make a wooden device in his favoured shape, and claim full bonus!)

Caribet is exactly right. By these rules a Verditius's lab total will typically only have their Craft score as a bonus above and over other Magi. Other Magi will probably try to get a bonus from the effects of the materials used, up to their Magic Theory, thus effectively getting twice their Magic Theory. A Verditius (with a high enough Philosophaie) can get twice their Magic Theory using anything pretty much, and get ther Craft as a bonus, and lower the Vim vis required also by an amount equal to their Craft score.

By far I'd say it's the best interpretation of Verditius Magic yet. Previous editions merely gave them an Ability called Verditius Magic which added to your lab total and that's it. I can't wait to see the Inner Mysteries of Verditious Magic.