What software is generally used in industry to design cases for pcb boards?
Generally, you need software that can export STL files.
Solidworks: $4000 + $1300/year
ProEngineer: $5000? + something per year?
Autocad Inventor: $5200? + something per year?
Google Sketchup: Free or $500, but can't export STL directly. I've seen mention of a plugin that can convert Sketchup files to STL, but I haven't used it myself.
(From Peter Gibson) Blender: Free, but alleged to have a steep learning curve.
Take a peek at Alibre Design. It's more affordable than the other options, and has a free trial. I bought it recently and I'm very satisfied. Not only it meets all of my needs, I compared it to Rhino, SolidWorks and others and found it way better, both in capabilities and user interface.
I would also recommend Alibre Design PE, which is a bargain at $100. I'd also like to add another option that is free (just like Blender), called OpenSCAD. It is highly capable, and for doing simple PCB enclosures, I would pick it over Blender anyday because it's so much easier to understand. In many cases (pardon the pun), I would use it instead of Alibre Design because you can share your designs more easily with the community. It exports STL and DXF as well. There's something really cool about changing a few variables in the code that generates your model, and getting back a new part that fits a new PCB. Tweaking due to measurement errors is just as easy, provided that you wrote the code properly.
Apparently K-3D also does STL export, and it's quite a lot easier to use than Blender.
You can use FreeCad
According to their site:
FreeCAD is a general purpose parametric 3D CAD modeler. The development is completely Open Source (LGPL License). FreeCAD is aimed directly at mechanical engineering and product design but also fits in a wider range of uses around engineering, such as architecture or other engineering specialties.
FreeCAD features tools similar to Catia, SolidWorks or Solid Edge, and therefore also falls into the category of MCAD, PLM, CAx and CAE. It is a feature based parametric modeler with a modular software architecture which makes it easy to provide additional functionality without modifying the core system.
As with many modern 3D CAD modelers it has many 2D components in order to sketch 2D shapes or extract design details from the 3D model to create 2D production drawings, but direct 2D drawing (like AutoCAD LT) is not the focus, neither are animation or organic shapes (like Maya, 3ds Max, Blender or Cinema 4D), although, thanks to its wide adaptability, FreeCAD might become useful in a much broader area than its current focus.
I had the same need and went with SpaceClaim.
Alibre, Autodesk Inventor and SolidWorks share the same basic philosophy with increasing capabilities and cost. They are all in my opinion old-fashioned, clunky and takes a lot of time and effort to learn.
The reason we went with SpaceClaim is that it is much easier to use, you can work entirely in 3D if you want, you don't have to go back and forth between 2D and 3D. It is not history-based, meaning it "understands" most geometry better. Most other modellers rely on history and without the history you often have to recreate a model from scratch if you need to edit it. SpaceClaim also includes IDF support so you may be able to import your PCB and design around it. SpaceClaim is less expensive that SolidWorks or Inventor.
Before SpaceClaim we used SketchUp, which is similar in terms of ease of use. I like SketchUp a lot, but it is not a solid modeller and is lacking in precision and features. But it's great for its price if you are ok with a surface modeller.