Also, don't miss this little thread
viewtopic.php?f=9&t=635The inkscape extension mentioned in the above thread is probably ok if you take any of the map1-3 or insularComplex as a basis for your custom map.
Map4 represents the latest ways in map editing, with custom surface and terrain layer configs, so if you're interested in those, you are better off with the inkscape extension INCLUDED in 0.73 release, under tools-subfolder.
I intend to migrate map1-3 and insular to the new way too at some point, but it's not the first thing on my mind right now.
About destructible buildings, there has been some discussion about it during the past 12 months I'm pretty sure, and I'd recall the main issue with that being how to deal with interiors that are then visible if buildings are partially destroyed. Basically, you should be able to see someone's living room and kitchen there, with couches and tables and other details, so it would become quite a huge task easily outside scope of RWR.
With some heavy simplifications, by having interiors mostly black perhaps, or making sure interiors are not seen, or that buildings would collapse completely floor by floor, I wouldn't see why destructible buildings would be completely out of question.
Editable terrain would be a slightly more straightforward task, again with some simplifications, e.g. it wouldn't be possible to dig caves at all, that's simply not supportable.
Destructible walls and fences, however, will happen for sure. That's something I definitely want to see as well.