You want your customer to have the possibility to choose between different shipping methods and they should automatically vary from size to size?
It is that easy:
Hit "shipping methods" > "Create new shipping method"
Enter a name (standard delivery/ expedited shipping/2-day-delivery...)
Authorize chosen countries for the method by searching them in the drop down menu
If not already done hit "zone configuration" to save more country groups
Enter a fee for using this shipping method and set the weight range for this method so that it will be just displayed for matching products
Don't forget to mention the approximated time the shipping will take in the description (Tip: Don't gloss over but be as precise as possible)
Save and you are finished:-)