My second building project... this one took quite a while, building in the evenings after the kids went to bed.
The playhouse is based off of Ana's Playhouse Building series, with some modifications to fit the space in my backyard and accommodate climbing wall, monkey bars, and slide.
To put the main deck structure into the ground for sturdiness while protecting from moisture, I dug out 5 holes to fit single hole cinder blocks (4 corners plus an extra 4x4 for the monkey bars; you can see an leftover block on the ground in one of the pictures). I placed some brick in the holes, then the cinder blocks on top. I then partially filled the cinder blocks with sand, put the pre-built deck in the cinder block holes (with help - it's heavy!), and then filled the rest of the cinder block holes with sand. It's worked remarkably well - the deck has been up for about a year now. I also sprayed some clear waterproof sealant on the bottom part of each beam near the ground for extra protection (deck, monkey bars, climbing walls, and swingset A-frame). This has allowed me to still run sprinklers near/around the playset and even grow grass underneath the swings!
* Playhouse: pine, plywood, Suntuf solar grey polycarbonate corrugated roofing panels (I live in Arizona, so little rain to worry about but lots of heat - the sheeting lets light in but blocks most of the UV rays, corrugated shape also provides venting at top when placed sideways)
* Deck/Swingset/Monkey bars: treated lumber, composite decking, pine for railings, monkey bars purchased from Amazon
* Climbing wall: pine, treated lumber, handholds/railing bought off ebay/Amazon
* Swings/slide/bongos/wheel, telescope: purchased from Amazon
* Turned playhouse 90 degrees to be in back of the deck, with swingset coming off the side. This meant the support beam for the swingset had to pass through the playhouse - modified the frame for that wall slightly and created a notch for the beam to pass through.
* Slide comes out one end of playhouse - made the "window" on that end larger than the plans called for in order to give room for the slide.
* Monkey bars come off one side of the deck - used extra 4x4 here to create support for the bars, and used extra bars to make a ladder on this side
* Climbing wall instead of ladder for main entrance
* Put large window in back wall of the playhouse
* Added cross bracing to side of decking on swingset end to make it more solid/cut down on sway when swinging