Measure areas between the top of the doors and ceiling (in this example, that covers two corners). Then, measure the other two corners from floor to ceiling. Cut a 4 x 4 pine post to length. (This will prevent the logs from being mitered for the corners).
Place a short 4 x 4 post over the door, pre-drill holes on the sides, against the walls. Attach the post to the wall using 2" wood screws.
Pre-drill several locations along the sides of the room and "tack" the 4 x 4 posts into the correct locations for the siding to butt into.
Install the baseboards. Measure between the corners, then cut pine 1 x 6 to fit the space. Check for level, then use a pry bar to adjust as needed. Secure to wall with 2" trim nails. Work around the room to attach baseboards until completely installed.
Figure out the height from the top of the baseboard to the ceiling. Determine height of plank. Divide the height of wall area by height of plank. This will determine if you need molding installed near the ceiling. If the gap at the ceiling is greater than 3-1/2", simply rip the paneling to fit. Install without top trim. If less than 3-1/2", add trim for 2 x stock to fill the gap.
Next, use a stud finder to determine where the log siding will be attached. Use a marker to mark the studs from floor to ceiling.