The Virtual Robotics Toolkit does not yet include a building environment. However, the software has the ability to import 3D models that are created in LDraw format.
There are many great CAD tools for creating LDraw models, a few of which include:
- LEGO Digital Designer: http://ldd.lego.com/en-us/download
- MLCad: http://mlcad.lm-software.com/
- LDCad: http://www.melkert.net/LDCad
You should also consider installing the LDraw 'All-in-one-installer', which will give you a near limitless library of bricks and color combinations.
The LDraw library can be downloaded from: