Alex McDowell recommends using Previs before finalising designs because he feels it is easier to mock up a quick 3d model rather than sketching a lot of designs when first discussing ideas with the director. The model can be used to consider camera angles and make quick adjustments. The key selling point of Previs is the speed and ease of use when creating this model as opposed to traditional drawing.
Google Sketchup is a free, open source program that allows users to download and modify the work of others. I wanted to see how easy it was to use by creating a workable model when having no experience of the software.
On Wednesday 16th April I sat down in front of a blank document without any idea of how to begin. I drew a rough shape of the room I wanted onto the axis, then immediately googled how to extrude the shape into a 3d form. I found a tutorial right away was able to make the room I desired.
After learning how to add/change textures and download components I found the Google Sketchup to be very simple and even addictive.
I do see the benefits of working in this way. There are limitations to the design but as an initial stage of the process it is very quick and flexible.
Below is an example of a Sketchup model used by Alex McDowell for the film Upside Down (2012).