In my early days as an architect, I used to model a lot, mostly with AutoCAD, then rendering with Lightwave through 3ds files. I even played with Mechanical Desktop, a parametric, resource eating behemoth. Unfortunately all that software was crack, and I’m not confortable with this anymore. I gave up modeling in the last ten years, but if I were to recap, there is a powerful open source alternative: Blender.
Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing and motion tracking, even video editing and game creation.
I messed around a little bit with Blender, and it really is a great parametric modeler. It just has a pretty wierd user interface, and the hard part is to get used to it. The software is written in Phyton, it runs on every platform and has a really small footprint on your resources.
Blender 3D Architect
Blender 3D Architect is the place to find news, tutorials, resources and training related to architectural visualization using Blender. The authors have a passion for architecture and technology and all the possibilities that Blender can offer to new and experienced artists. Here you will find on a regular basis, resources, and artwork from artists from all around the world.
The site offers pretty good tutorials. I signed in for one of them, and stumbled upon a great piece of software: Archimesh.
Archimesh was a Blender add-on for creating architecture elements, and is now part of Blender official releases. Archimesh makes it very easy to model walls, stairs, windows and furniture. All the elements are fully parametric, and you can modify them at any time.