Alex, please don't take this the wrong way, but just how long
is a piece of string?
- Who does usually decide about the construction method (e.g. bricks, wood, steel) to be applied in projects?
The Owner/developer may well have their own preferences,but in general on commercial builds it's the architect who decides, based in part on the brief from the owner/developer, and often with additional input from both the structural engineer (engineering design of stressed components) and the quantity surveyor (outright cost). There is also a large amount of input from the local council (planning restrictions, zoning, etc) and statutory regulations must also be observed. Finally amendments may well be required when the building contractor comes on board (he/she can make recommendations to improve speed/cost of build) and there are inevitably variances during the build brought about by details which the architect may not have designed fully
- How many persons do you need on site to build the set of walls with your standard method (bricks, wood, pre-cast, steel, in-situ concrete, other)?
This is the how long is a piece of string..... For a commercial building you'd also need to consider steel framing
with cladding (this is often combined with masonry at the bottoms of the walls, primarily for security/durability). These days there are alternative materials such as straw bale, SIPS, masonry cladding over timber frame, etc to consider not to mention pre-manufactured timber framing. Each has it's own labour/skill level attached and the number of people required on site to build any walls is influenced by factors such as the build schedule, interaction with other trades, etc. Each project can be very different
- How many persons do you- How many days does it take you on average to build the walls of such one-storey buildings with a floor area of 100 m2 (excluding the foundation, slab and installing windows)?
What type of wall is it, how tall is the wall, will the wall surface be curtain walling or structural ? (in which case what loading is it going to carry?) The height also impacts on other costs in the build; for example a steel-framed portal building can be assembled without scaffolding, but using cherry pickers/scissorlifts for access at height whereas a timber framed building or anything with masonry cladding will require scaffolding to be erected (sometimes portable towers, sometimes system scaffolding). All this impacts on the time and cost of a project
In terms of labour, also note that most trades work as 2-man or 2 + 1 man teams. This is often not only more efficient than employing individual tradesmen, but in some cases (e.g. working at height, in harnesses, etc) can be a legal requirement
Without knowing in much greater detail it is impossible to give you the figures you are seeking. The best I can do is to point you towards the Quantity Surveyor's "pricing bible", Spon's, which quantifies many of the items you are interested in, however there Spon's is a sort of "best guess" as building materials and methods are constantly changing
