I have thought of this in the past and it's not all that hard.
Basically the round logs are used in instead of bricks or rocks.
R value of wood varies by type of wood. White pine is supposed to have an R2 value per inch so a 12" wall would be R24 in theory ? Ya, R24 would not be correct at all. Only the wood has the R value, not the masonary filling in the gaps between logs. This of course applies to any wood or R value. If your wall is 75% wood and 25% mortor holding it all together, then what is the R value?
Start with good clean log sections of the lenght you want, say 24" for a 2' thick wall.
Debark all the pieces and let season/dry. Wood shrinks when it dries and you don't want it shrinking after you build a wall and it has been mortered in place, that's why alot of log homes crack out the chinking the first year or 2, the logs were not aloughed to dry and shrink enough before chinking them.
I like Picsters log homes, Scandanavian Scribed logs. That type does not need the mortor chinking and as the logs shrink the home becomes much tighter and seals itself basically. Thats real log house though, not cord wood.
As with any masonary work, the walls should be built so that it would hold together just the same even without mortor. In other words, you should NOT use mortor to glue the wall together, the wall should stand on it's own. Mortor fills in the gaps and helps hold things in place, but it is not supposed to keep it from falling apart. I see many "supposed" professionals building rock walls, they don't have a clue! They glop on mortor and slap down any rock not carring rather it actually fits, then glop down more mortor and another rock. In 2-3 years (maybe sooner) the wall starts falling apart and they claim it was because the owner did not have the wall back filled correctly and the pressure from the ground broke it. That often is not true but sometimes it is. Many times it is because the wall builder did not fit the rocks together. Any Masonary work should be considered a gaint jigsaw puzzle of odd shapes, find the pieces that fit the holes! If the mortor were to fall out or be washed away the wall should still stand on it's own!! That includes any type of arches for doors or what ever.
Course block or brick walls are all flat sided other than arches or such and don't actually count. But rock, logs or what ever, find the peices that fit to build a self standing wall and mortor those into place.
Mortoring logs. They should be seasoned air dry, normal moisture content. Lay a bead of mortor on the inner and outer ends of the logs, perhaps a few inches in from the ends, dampen a dry log with a wet rag and tap into place in the mortor. Wetting the log slightly prevents the log from sucking the moisture out of the mortor, something you don't want to happen, it also helps to create a better bond. Use should also moisten blocks, bricks, rocks or whatever if building with those. Again I see "supposed" builders laying them up dry all the time, then wonder why morter cracks latter.
If you want you can fill the space between the mortor beads with a strip of fiberglass insulation for better wall R values as you lay the logs. This would be good for housing, not needed for a large shed or barn probably.
Waxing the end of the logs will seal them and help to keep out moisture and bugs, other things can be used also.
Well I gotto run, someplace to be soon. Buying books on how to do it right is a good idea of course and finding people that build them right that you can learn from is great too. Perhaps the above I wrote will help those building smaller buildings or even homes that don't have books or such to learn from. How you start a wall and what you build and such varies alot by design. But that's the basics of building a wall.
Dry the wood, debark it, find the piece that fits the hole, dampen it, lay 2 beads of mortor, tap log in place. Seal the ends to prevent bugs and moisture. Using fiberglass if desired.