We actually tried this web first on my balcony at the apartments I live, then decided to try a much bigger version at Hallowbean's house! It goes well with the giant spider. It is a relatively cheap and easy prop that really makes an impressive yard prop. We used about 400 feet of white rope and a poseable spider, both items were from Wal-mart.

We started with 4 ropes strung across the yard. One rope is looped over the others in the middle, to make a good center point for the web.

 

Then tied an end of another rope near the center.

 

We then start wrapping around each strand, making a spiral pattern. To keep the rope from sliding down, you may need a knot or a piece of tape to hold them in place.

 

Another shot of the spiral we're "weaving".

 

Near the finish of the web. With more rope, one could actually put these strands closer together.

 

A finished shot of the web. The spider in the center of the web was from Wal-mart, then of course on the roof we have our giant spider.

 

Don't have a house with a big yard? You can still do a nice web. This is my balcony in Orem. Giant web, with a skeleton rappelling.