This is an easy to build Frontier type playhouse that your kids will enjoy.  The design concept is so unique that I will let you look at the picture above to contemplate nailing all those "logs" on the building and then ask me why I said this would be easy to build.
Now that you've looked over the photograph, I'll reveal the unique design of this playhouse that makes it "easy to build".  We use 6ft x 8ft sections of stockade fence as our walls....right about now you're slapping your forehead....what a good idea!  This reduces our work to cutting out windows and doors from existing fence panels. Note: All materials are pressure treated...even the plywood floor and roof. Try to purchase 5/8" pressure treated plywood for floor and roof.  If not available, purchase 1/2". Step 1.  Make floor joist frame by using 2x4's.  Follow measurements below.
Step 2:  Install plywood floor on floor joist frame.  Plywood is installed sideways.  Floor joist spacing in drawing above allows front wall of playhouse and plywood seam to hit a supporting joist.
Step 3:  Make left and right side walls by cutting fence sections per the following drawings.  You are going to make a few modifications to some of the fence panels to make them work. Such as: Move some horizontal fence support boards to new locations and reattach. (where shown too) Cut every other end off vertical fence boards to allow interlocking of boards at the corners. Add door and window framing to inside of some fence sections. (where shown too)
Important Caution: Measure and cut the two side panels as shown on the right. Do not cut the front and back panel ends off without verifying starting point.  In other words your front and back panel cut off (log ends) need to be the opposite of the side panels so they will interlock. If point "A" at right is cut off on the sides, then the corresponding first "log" on the front and back panel will be uncut.

Step 4: Next we will work on the front and back panels.  On these panels you will need to move the horizontal support boards as shown on the drawing below. The next step will be to measure cut and install additional framing to support windows and doors per drawing on the right.	The drawing shows 1x2 framing around windows. If you choose to do this you will need to rip it from 2x4 pressure treated lumber.  You can also substitute 2x2 pressure treated for the window and door framing.
Step 5:  Assemble walls together fastening horizontal (now vertical) fence support boards together with 3" galv. screws at each corner.  Place 4 evenly spaced screws in each corner.
	Step 6:  Frame porch roof.  Start by fastening 2x3 board to front wall directly above front door  trim to attach front porch roof frame.  Use 2x3 for front porch frame and support posts.  Porch posts will be 4' 6" long as shown.  Install  roof frame to playhouse. Cut and nail plywood roof sheathing to top.  Install double layer of 30 pound roof felt or shingles.
Step 7: Install 2x4 roof supports across the width of the playhouse from wall to wall. Install at 16" spacing, and fasten to top of side walls by nailing (16d nails) or installing screws through side wall "logs"  into end of 2x4 's. Roof supports (2x4) should be installed with long measurement (3 1/2") vertical.  Step 8:  Install sign above porch roof if desired.