3D printing an AEC model often requires combining different 3D models. This is known as 'geometry integration'. A common case would be combining a house that was modeled in one program with the terrain upon which the house will be built, modeled in a different program. There are many, many different CAD modeling programs, thus there are a large number of challenges with regards to geometry integration. Further complicating this issue is that the final result must be a single, solid 3D printable file.
While it is impossible to specify a best practice for every combination of CAD models, there are certain techniques that work better than others. Below you will find some user-contributed accounts of successful geometry integration, regarding specific programs. The key is usually to find a file format that both, or all, involved programs can share.
Users are encouraged to share their geometry integration experiences and knowledge in blog format. Also feel free to post to the forums if you are struggling to integrate geometry.