I'm not a loop user.. I've just had a listen to 2 versions, Muddy Waters and Buddy Guy.
For me I think it's easiest to use Session Drummer 3 or Studio Instruments Drums to program / build up 4-beats patterns. After one pattern, you can copy/paste and edit from there.. just don't forget to un-link the pattern first after pasting - else your edits will effect the original pattern too.
The drums are slow enough for you to do part by part.