If page numbering ever happens in LO you might be given the option to add prefixes to your page numbers. This is possible to do in InDesign and you could arrange page numbers exactly as you have described below - with a chapter number prefix for the type of drawing (1 for site plan, 2 for floor plan, 3 for section etc) and then the page numbers could be generated as you add pages. Its a really handy feature of indesign and would be really handy in LO - but as Gaieus said this has been asked for many times, just hoping that if its said enough the next release of LO might include this feature and save me having to manually do it!