I found this youtube channel[0] has some pretty good walkthroughs (quite literally) of using various iOS apps to scan architectural spaces. The short answer is that the LIDAR and iOS APIs are remarkably powerful, but not 100% accurate. There are techniques to improve accuracy (e.g. using a gimbal), but ultimately you'll need to do tape or laser measurements and modify the models that these tools can build, or just model it yourself with the scan as a reference.