I got an in-world IM from Vivienne Daguerre about free copies of Hexagon 2.5, Bryce 7.0, and Daz Studio 4 Pro. The free copies will be available for the month of February. Vivienne did an evaluation of the software and offer.
See her article here: Hexagon 2.5, Bryce 7.0, and Daz Studio 4 Pro–Free!
I’ve downloaded the programs but haven’t taken the time to start playing with them.
You can try SketchUp. It is a nice 3D designing software. and it is also free.