Any Advice On Play Time Outdoors?

[Watermelon-Pets]

Very soon I will be a guinea pig owner, which I am really excited about. I am pretty much prepared, just a few things I can get round at my local B&M. So I have an outdoor hutch ready. I wanted a hutch with a run and a bit more space but I didn't have the money to get it on such short time (I only found out about the guinea pigs on Tuesday and they are arriving on Saturday). So I am going to slowly introunce them to my lawn, I don't won't to stress them out but they should enjoy a run around. I have alot of hideouts for shelter and toys to use but my garden is extremely secure from escapes, predators, lost guinea pigs. So If I can get them out everyday building up the time gradually, would I need a pen? I was going to get a run to attach to the hutch but we have raised the run to put storage underneath. So unless they have a ramp down (which I read some piggies aren't great with ramps) into the run, I can't do that idea. I could make a good sturdy ramp that's not steep and put sides on it, and attach it to the hutch. But would this work?