I work in the lumber industry as a Lumber Inspector, any wood that has not been either air dried or kiln dried is considered "green". General Rule of Thumb for Air drying is 1 year for every inch of thickness. Poplar is a great wood to use for siding, flooring, and framing. The only recommendation I would pass along is to have either white oak or treated wood for what ever parts come in contact with the ground or foundation because Poplar will rot if it stays moist. If you are just going to put it on runner/skids then I would try to use white oak if I could get it and build up from there using the poplar. I also agree using the board and batten style of siding will prove out to be most efficient. Reason I recommend this, one all wood moves and if you happen to use some wood that hasn't dried completely it allows the wood to shrink or expand without popping the boards. Also replacing a board is easier like stated earlier. We generally figure on a board shrinking from a 1/4 to 1/2 inch depending on what season the log was cut. Spring cut lumber will shrink more than Fall cut lumber due to the increase of sap in the log. Also keep in mind, a log will never completely dry out no matter how long it lays once the tree is cut. It will loose some moisture but minimal beyond the ends of the log where air can come in contact.
