Just had a patio "half" installed by some contractors. Due to issues with their measurements, we have to wait for more materials to arrive. The patio caught my eye earlier as I thought it looked a bit out of level, and so have just gone to check it. I have pictures attached, and am considering witholding payment for this part of the work unless it is rectified. Just wanted to get other people's opinions before I do anything drastic. Just for reference, the garden slopes from left to right at about a rate of 1-2mm per meter, so basically level, and slopes away from the house at about 5-10mm per meter. The overall drop on the laid patio seems acceptable, however is not uniform and has resulted in dips and raised portions which concerns me with regards to flooding. What do you guys think?