There is a careers section at this link, and the link also takes you on to the National Construction Colleges Prospectus 2004, City and Guilds, etc. There are no one day courses anywhere in the country that would let you try out being a bricklayer, carpenter, etc. for a day, but plenty of career advice is available through the CITB, who might be willing to arrange a visit for you visit an active building site to see the physical work of the main trades and view working conditions. There is also the Building Book Shop, 26 Store Street, a turning halfway along Tottenham Court Road, which has descriptive books of every construction trade.