What's this spider?

Can you identify this small spider for me? He is about 1/4 inch long and sits in the middle of a mostly-horizontal, tiny web. There are long strands in the web that lead upward and attach to higher objects (almost like he's sitting at the base of a tent).
There seem to be many messy layers in the entire web triangle. It's a very complex home for such a little guy. If the spider is disturbed he runs under the closest object. My guess is either a sheet web spider or possibly a small wolf spider.