The building owners are fishing for a cheaper deal. a sound access method will have to be drawn up by whoever you use to abseil this building, the louvers look like a right pain because there obstructing easy access to the windows, also damage to the aluminium on this building could be quite easy with a team of heavy handed abseilers and could work out very costly to repair, so make sure your choice of subcontractor carries out the most thorough survey and has some very good insurance and be careful not to under price this job.