Hello,
to provide a cheaper shipping, I would like to offer different services.
We have something like this:
If the package (length + width + height) is less than 90cm then it could be shipped by company 1.
If it is bigger, it must be shipped with company 2.
Now for both companies the weight is important - so I just need to sum up the products weights and I (or Ubercart) has the price.
But how about the size? Could it work, that I tell Ubercart, that is a small product and if I have like max. 20 small products use comp 1, if more, than comp 2.
Difficult to calculate I guess 
Thank you in advance
Chris