[Search] Freeware 3D Modeling app with measurements

Hi,
I'm looking for a freeware application which allows me to create 3D models using measurements.
All I'd like to do is to scale an object based on values.
Example:
Create a box and size it to 30cm x 20cm x 50cm

Thanks in advance for any input!

regards
Xarthor

http://www.rab3d.com/tutorial_started.html Is this what your talking about? (scroll down on this page to blender units and precision)

First of all: Thank you!
Looks like I haven't looked really into Blender, but I just downloaded it and I should be able to use it for my needs.
Thanks again!

yeah with blender when to scale, move or rotate something you can either use the mouse or type in your own units and press enter for specific values