Moisture and Logs
The most important piece of advice I can give someone about to purchase a milled log home is to buy dry logs!  There is much said and written about designing and building to accommodate for the shrinkage and subsequent settlement associated with using green logs.These methods fail as often as not. A structure that moves as it dries is a machine.The driving force of that machine is gravity.The weight of everything supported by the log walls is the amount of force available to cause settlement in the log wall.This is a rather small amount of weight acting upon each lineal foot of log.                             
     The machine in settling is trying to overcome anything that may cause the logs to "hang up".  Friction of twisted logs on fasteners,walls, trims and bucks must be overcome.  Caulk is essentially an adhesive.I have seen it shear wood,this happens at about 350 PSI.   Any  misplaced nails hold up around 250 pounds each.  A timber that chooses to bow while drying can often support thousands of pounds before flattening out.
     Conclusion: for most homes the driving weight of the roof is simply insufficient to overcome all the small but cumulative "hang ups" that occur.  Do settlement sytems work? Not reliably enough for me to build with green materials! Should you build with a settlement system? It couldn't hurt. If you wish to try to accomodate the amount of shrinkage that occurs from 15%-19% at purchase to 8%-13% at equilibrium in service,by all means go ahead.  Don't ask these systems to accomodate 30%-50% logs.
Below: A freshly cut log end showing a dry shell and a wet core. The logs appeared dry.The lighter colored wood is below fiber saturation point.Moisture (free water) has left the cell cavity (lumen).Much moisture still remains in the cell wall as bound water. The darker wet wood is above fiber saturation point. Lumens are still full of free water,cell walls are full of bound water. Wood shrinkage begins after free water has left and  as bound water leaves the cell wall. Top Right: 42%,Bottom Left 45%. Bottom Right:Tightening a lag several inches away in a piloted and countersunk hole, water running out  through the end grain.
How Much Will My Logs Shrink?
The links below are to an Equilibrium moisture content calculator and a shrinkage calculator.

First you will need to know the relative humidity inside your home. If you need a worst case number to plug in my home is wood heated and in midwinter we run 45% RH at 65 degrees F.

Take the information from your home to the Equilibrium Moisture Content Calculator and then return here with that number.
Wood is always gaining or losing moisture to its surroundings in an attempt to be at equilibrium with the surrounding humidity and temperature. This is why doors stick in the summer and rattle loosely in the winter,the wood is shrinking or swelling as it absorbs moisture from, or, evaporates moisture to, its surroundings. These seasonal changes are small in comparison to the amount of dimensional change wood goes through in drying from the green condition. Using logs that are dry Guarantees that shrinkage that happened in the kiln is shrinkage that doesn't have to happen after the house is built.  Dry logs have normally bowed, twisted and checked (cracked) about as much as they are going to.  When a good looking DRY log is placed at eye level in the living room it will remain a good looking log, with a green timber it's anyones guess what will happen as it dries.
   Arrive at a moisture content for your logs that both you and your supplier can live with.  Remember drying takes energy expect to pay more for this.  Get it in writing! Tell the manufacturer you will check the moisture content before accepting the load. Then do it!  Even if you need to purchase a moisture meter just for this one house isn't $500 worth it?  Every other piece of wood in your house is required to be below 19%, shouldn't the logs be also?   Building with green materials is simply too unreliable, don't be lured into doing it.
Equilibrium Moisture Content Calculator
With Your EMC number in hand ,go to the Shrinkage calculator below and plug that information in  under final moisture content
Find  the wood species you intend to use. If you do not know the moisture content of the logs you will be purchasing use 28% as a starting point, otherwise plug in the moisture content agreed to in your contract.
Also you will need to plug in a  starting dimension. If using  8x6 milled D logs for instance one would type in 7.25" (for their actual starting dimension).
Or plug in 96" if you wish to see shrinkage in an 8' wall.
The output will be the final dimension of the log or potential for settlement in the wall when the wood has reached equilibrium.
Shrinkage Calculator
read about shrinkage and moisture content
More about shrinkage and moisture content
Shrinkage values