Thursday 1 August (7pm)
@ Trafalgar Square, Tube: Charing Cross
Price: FREE
Links: osa (office for subversive architecture)
Surely you can't have anything better to do?! Tonight, osa (office for subversive architecture) will be issuing about 250 people with an umbrella and a suit each, in order to make a giant roof over Trafalgar Square. Osa is getting a reputation for this kind of thing now - its last project saw a public subway transformed into a domestic flat. The umbrella offensive, called London Roof, is an installation that refers to the timeless and ephemeral qualities of architecture. Mostly, it aims to challenge the meaning of "space": The roof is not about a fixed and built space, but a fluid space relying on public participation. The umbrella, says osa, is "the most practical and utilitarian object used in London, it represents a potential architectural module, and is used by approximately 8 million inhabitants of the city." If you want to join in, email Bernd Truempler at btruempl@fosterandpartners.com - let's just hope it doesn't rain.

NB: If you have an umbrella it also serves as the ticket to the after-party - at Oporto Bar, 168 High Holborn (020 7240 1548), WC1.