While there are many companies who make and sell wood playhouses, they can be expensive and deprive you of the fun of building one yourself for your kids or grandkids. Instead, consider building it yourself.
Decide on the basic features you want for the playhouse. Plan the number of platforms, swings, slides, ladders, pirate wheels and such your kids would want to have. Take into account the current age of your children and how the playhouse can grow with them.
Download and print the free playhouse plans to follow. A few companies offer free building plans for playhouses, which gives you the peace of mind of having a sturdy structure without all the measuring and designing. One such site offering building plans for playhouses is Free Wood Working Plans. (See Resources)
Check out the materials list for the plans you have downloaded and printed. Some will be very specific on the wood to use for certain areas of the structure, while others will allow you the creativity. You want to use a wood that will be strong like pine or will take stain well like ash.
Consider the coloring, treated vs untreated and other aspects. Treated wood will last longer and the chemicals used in this are not harmful to play on or around. Consult with your local lumber supplier if you are worried about this. Also, always ask for a bulk discount if purchasing all the needed lumber from one company.
Contact your local lumber mill and meet with the sale department to get a quote for the wood. They can often offer you a discount for bulk orders, or help you decide the perfect wood for the job. Also, figure in about 10 percent overage for mistakes or last minute add-ons.