Method for building an elevator system in an elevator shaft of a building that is in its construction phase, in which method a usable lifting height of the elevator system is adapted to an increasing height of the building, - a machine platform being installed in the elevator shaft, which platform can be raised and temporarily locked along car guide rails, and on which an elevator drive machine having a traction sheave is arranged, - an elevator car and a counterweight being suspended from the machine platform via suspension means, the suspension means being guided at least over the traction sheave of the elevator drive machine, so that the elevator car and the counterweight can be moved up and down in opposite directions to one another along guide rails (6, 7) in the elevator shaft by the traction sheave via the suspension means, - a lifting platform that can be raised and temporarily locked in the elevator shaft being installed above the machine platform, by means of which lifting platform the machine platform is raised with the elevator car or the counterweight when the usable lifting height of the elevator car is to be adapted to a current height of the elevator shaft, and - before the machine platform is raised, the lifting platform being raised to a higher level by means of a construction crane or another lifting device, characterized in that the lifting platform is equipped with a cable catching device (25.1; 25.2) which comprises a safety cable which is arranged between the lifting platform and a cable pulley support according to the principle of a pulley block having at least two load-bearing cable portions (31.1-31.4), which is fixed above the lifting platform in the elevator shaft, a first load-bearing cable portion (31.1) of the safety cable being fixed to the lifting platform or in a stationary manner above the lifting platform, and a last load-bearing cable portion (31.4) being guided through a cable stopping apparatus which is fastened to the lifting platform, by means of which apparatus the last load-bearing cable portion is blocked and, as a result, further lowering of the lifting platform is prevented, after the speed of the last load-bearing cable portion (31.4) relative to the cable stopping apparatus has exceeded a predetermined limit. - a machine platform being installed in the elevator shaft, which platform can be raised and temporarily locked along car guide rails, and on which an elevator drive machine having a traction sheave is arranged, - an elevator car and a counterweight being suspended from the machine platform via suspension means, the suspension means being guided at least over the traction sheave of the elevator drive machine, so that the elevator car and the counterweight can be moved up and down in opposite directions to one another along guide rails (6, 7) in the elevator shaft by the traction sheave via the suspension means, - a lifting platform that can be raised and temporarily locked in the elevator shaft being installed above the machine platform, by means of which lifting platform the machine platform is raised with the elevator car or the counterweight when the usable lifting height of the elevator car is to be adapted to a current height of the elevator shaft, and - before the machine platform is raised, the lifting platform being raised to a higher level by means of a construction crane or another lifting device,