Outdoor work areas

Attached is a work in progress cad of the outdoor work shed im cad-ing.

Background: My team doesnt have a full classroom to work in, our room that we use now should really be converted to an assembly room thats cleaner and we are comfortable with our on-board electronics in. Good news, we have a massive patio thats enclosed by stone walls and a heavy gate! My team wants to utilize this space for working, ie. cutting drilling, all the dirty stuff. My mentor wants to just have a covered work area outside, as in a tarp or roof, but no walls. I see a problem in this because even if we paint the workbenches, i feel like the elements would still get to them in a significant way, also I dont think anyone wants to have their drill press, cold saw, or really any type of tool at all, outside, so it would limit us to easily moveable tools, like hand saws that we would have to take outside every day. Cost is on his side, but it is something that we may or may not ignore pending debate, im giving the team a sizeable chunk of change that will easily cover the cost of this. Space is probably the only thing that will be an issue, and its something im worried about too. Currently this design is ~15x20 feet. We are living in San Diego btw.

Question 1: Covered work area, or full on work shed?
Question 2: What do you think is an appropraite size for a work shed if we do one? essentially any work that isnt us turning a wrench or doing electronics will be out here.
Question 3: how closely do you guys think floor supports need to be? im going off a guide that says ~15 inches apart, but its looking pretty heavy and expensive.

The guide im using, I made some modifications for the current sizing.

Oh sorry, I forgot my manners.