A method of assembling a structure of timber lengths, e.g. roof trusses, includes a number of upper and lower structure lengths or pieces, as well as a number of diagonals or braces etc., in which the timber lengths are laid out and fixed to one another. The structure formed from the timber lengths fixed to one another is observed by a first camera for positional determination of the structure and comparison of observation data with structure data and for controlling at least a second camera. The structure is fed into a unit for pressing in place of jointing pieces, e.g. corrugated fasteners, over the joints between the timber lengths by at least one positionable press unit, and the second camera observes the infed structure and positions the press unit at the correct position over a joint for pressing in place of a jointing piece.