Questions about building log shape and lengths.

 Some basic questions about log size in relation to building things like small sheds, boat and canoe sheds.  

  I have a small plot of land with a small house/camp.  I’ve been clearing the back section of mixed maple and spruce and saving the logs.  I’ve been cutting them to lengths I can carry and debarking them.  I’ve got most of the smaller trees out of the way and next summer will be felling the larger spruce trees.  There are about 10 tall spruce I could get some fairly long straight logs from.  Over time I realized that cutting lots of long logs say 12 -16 feet are too much to deal with by a single person.  I do not have any specific size building plan yet but ball park estimates are something like a low three sided shed for a canoe 18 feet long a 3-4 feet deep to tuck a canoe under.  A small shed 14 feet long 6-8 feet wide for a small boat.  A utility shed 8 x 10 or 10 x 14.

  I have collected 35 logs 6 to 8 feet of recent storm blow down from the side of the roads here (central western Maine) that are various diameters 8 to 12 inches.  
  I could build something with round logs or use the beam cutter to get logs with 1 flat, two flats, three or four flats for beam type construction versus all round logs.  

  How much difficulty will I have if I keep log lengths to say 8 to 10 feet build a shed 14 feet?  I idea to keep the lengths manageable so I can carry them.  I could cut a few longer sill logs and struggle with placing them but building a whole structure with long logs will be too much for me especially as the walls get higher.  I was thinking of keeping all cut logs 8 – 10 feet and joining them with pegs.  If I squared the logs to 4 x 4 or 4 x 6 they would be more manageable.  I could beam many after felling at longer lengths.  How feasible is it to go with joining smaller lengths?  Given the log weight would it be better to build with squared logs with 1-4 flat sides?