Making things with Rego.

I do not have City and Guild and I thing these rules are in that book.
I undertand you can make a house from a stack of lumber with Rego as long as all the ingredients are present, right? Nails, Thatch, etc...
Do you need saws, hammers, and other tools to be present also, or do you get to skip that part?

Check covenants, pg 49.

Yep, that right.

Right, you skip that part. No need of a corresponding ability too, just high finesse roll.

As a general rule, in terms of quality - Finesse -3 = your effective score in any craft at all. In matters of quantity of work done, rego spells can do the work of armies given sufficient duration and magnetude,

Actually, I think this is the strongest argument for studying/practicing Finesse.

Need to HOUSE an army for a siege? No problem. In fact, if you keep the individual barracks single-storey and simple, you can have 40 40-man buildings in no time at all.

A magus who has a high ReTe or ReHe as well as an affinity in Finesse can do some pretty spectacular stuff without vis. In fact, if you really want to make a magical builder (non-Verdiitius) try out the following:

Free Expression
Great Perception
Affinity Finesse
Puissant Finesse
Affinity Rego
Major Magical Focus (Buildings)

Give him or her 40 years post guantlet and be a long-term initiate of Hermetic Architecture.