I am trying make a layer of buildings, divided into apartments, by making polygons from crossing & intersecting lines in QGIS. When I use the vector/geometry tools/lines to polygons tool, I get just one polygon with no divisions at the inner lines, or otherwise odd polygons. The attached screenshot shows a random example of three polygons which were created, with the associated lines I hoped to use for the divisions. I also then tried the single part to multipart, but could not make that divide the polygon by the separate line file. I don't know if I am simply using the tools incorrectly, or if there is some setting I am missing.