It's well known that, nowadays, importing architectural or 3D designs from any offline program and reproducing them in SL is not possible. Nor dwg file, nor 3D Studio meshes, nothing at all.
We can only use the build menu in-world, which, though it is better than nothing, is limited in precision, just for naming one of its problems.

There are developments based on the Open Simulator project that allow to import obj formats, but they aren't compatibles with Second Life standard viewers (by now). One of this projects is the realXtend server/viewer.

In-world there are few tools to make the builders' work easier (aligning and filling hollows between prims), like Skidz Primz and Dockin Prims. But they aren't enough for complex buildings. SL architects have to make double or three times the same work: they use a CAD program to get their idea shaped, later they'll calculate how they can fill it with prims, calculating positions and modifiers, and finally, they will log in SL and build it. Again. With luck, their work will be finished in a few days.

Henshin system came up because of our (ai design studio) need of getting rid of unnecessary work. If we are already using a CAD program, why don't allowing it make the calculations and get "something" to build instead us in SL?

So, that is basically, how Henshin works: we design in Acad, which does the calculations. Once we are in-world, the generator will build while we are doing something more creative than inserting numbers in a box.

The version V of Henshin extends this concept beyond, not only allowing the use for Second Life, we can work for Opensim too. Much more... we are developing helper applications for allowing, even for people with limited knowledge of Autocad, the creation of complete designs: shapes, textures, physic and light properties, and, we hope soon, th "reimporting" from Second Life.

So, what are you waiting for? Test Henshin V (we have demo versions).