Blender is the most renown freeware 3D modelling solution.
I've seen good work in Sculptris if you're wanting to sculpt.
Although if you just want to learn you can actually download the industry standard Autodesk software for free with a 3 year license from the Autodesk Student site.
Out of those applications you should take a look at learning Maya or 3Ds Max (or both).
Here is a general summary some Autodesk Software:
Autodesk Maya - Modelling, Animation, UV mapping, Texturing. etc.
Autodesk 3ds Max - Modelling, Animation, UV mapping, Texturing. etc. 3ds Max and Maya are very similar and a lot of features are being transferred between them.
Autodesk Mudbox - Scuplting application, also good for painting textures directly onto the model.
Autodesk Motionbuilder - Animation, good for cleaning up motion capture data and making animations. Also links with Maya very well.[DOUBLEPOST=1380658529,1380658438][/DOUBLEPOST]
I'm not sure what you're doing with said model, but if you're going to be rendering a video out with it I would go with Blender, it just has an easier set up for cameras and such. I don't even know if Sketchup has the ability to render videos in it, I've never tried. If you're just making a basic model then I believe Sketchup may be an easier start.
Sketchup has no native renderer, and the textures are applied to world coordinates, you can't UV map models in Sketchup so it wouldn't suit his or her needs.