A building formwork component comprising first and second spaced sidewalls having one or more webs extending there-between, each sidewall comprising a flange extending inwardly along a first edge of the sidewall such that an outer surface of the flange forms a ramp surface; and a groove extending along an opposing second edge of the sidewall. The component may be coupled to a like component by relative movement of the components towards each other, whereby the flanges are received in respective grooves of the like component, and whereby the ramp surfaces facilitate such coupling by engaging respective second edges of the like component to move the second edges and/or ramp surfaces for engagement of the flanges in the grooves.