Seriously this is basically the last call to try to make something. Trenchbroom is easy and FOSS. All the tools are FOSS. Here's a tutorial:
Use any WAD pack, in reality the wad textures are not used and just serve as material names which include stuff like normal maps. Here's a good prototype WAD: https://github.com/jonathanlinat/quake-leveldesign-starterkit/raw/master/wads/prototype_1_3.wad