There is a large area in my backyard that was once a garden, but the previous owner let it go and it has collected a great deal of weeds and other detritus. Last winter we put tarp over a lot of it, and this winter we'll be tarping over the rest to prevent weeds coming up in the spring. And then, next spring, I plan to begin the "construction" of my own temple. I put construction in quotes, as there will be a lot more growing and planting involved then actual building!
The area is square, but I will be bricking off a small circular area in the center to be the main ritual site. Inside the circle will be a decorative pole (Sacred Tree in ADF), and at its foot will be a small birdbath (the Well for my ADF rituals), and a space for my larger cauldron that I also use as a small fire pit. Outside this circle will be a small circular bricked path, which will branch out like the spokes of a wheel, and it will be between the spokes that my garden will be growing. What I'm most excited about is imitating Stonehenge and other solar-aligned standing stones by building an astrological garden into the plans. For this I'll use small bricks that will mark the shadow of the pole at sunrise, noon, and sunset on the solstices and equinoxes; which should add up to nine bricks; they'll be inscribed with runes or ogham and half-buried. They'll be small and unobtrusive, but will represent a long-time project, and will connect my own little temple with the many that have come before. It will be relatively small, and probably wouldn't support a group larger than my children and I, but I think on its completion, it will be worthy of the name temple.
Obviously, not everyone has the time or the resources to make their own outdoor temple, and I can't even begin to express how blessed I feel to be able to do this. I hope my plans have been inspiring to some of you, and that you can find a way to make your own space into sacred space!
Sources: The 2012 Farmer's Almanac, on astrological gardens