A 3D home design using software that a DIYer can afford and use

I am building out the attic in my home with some dormers, and I would like to use home design software to generate a realistic 3D model that I can view and interact with from both the exterior and interior. I have tried to model the house using Home Designer Suite 2014 by Chief Architect, but I am having difficulty getting the software to do exactly what I want. I would like to have my current home structure modeled using 3D home design software, as well as two alternative attic plans that I am considering. The end result should be a couple of files that I can load in my own version of the home design software so that I can explore and further tweak the designs myself. I would prefer if the designs can be done in Home Designer Suite by Chief Architect, but I am open to other options as well (including the higher level editions of Home Designer), as long as the software doesn't get too expense (i.e., preferably not over $500). If for some reason it isn't feasible to implement the designs in any available DIY software, I would be open to having it done using more expensive professional software if there is at least some kind of free or inexpensive viewer that would allow me to interact with the 3D models (rather than just see a few static snapshots). However, I would much prefer the ability to edit the plans myself. I have much of the existing home already modeled in Home Designer (not including the attic dormers, and with a few problems that would need to be corrected). I could provide that file as a starting point, and I could of course provide all needed dimensions. An image of what I have so far is attached.