do they need shelter?

Depending on how many you have, a shed is usually appreciated. Lightening to trees has been known to kill livestock sheltering underneath the trees. And I have never seen a healthy sheep lying in the driving rain if a shed is available, so clearly they'd rather not be soggy.

And depending on where your line of trees are, there may not be shade available all day. Don't know where you are located, but in Virginia, they need shade in the morning through to sunset.

 

A shelter would be best, ask yourself if you would like to be stuck out in a thunderstorm/lightening/wind/rain and just have to be soaked. Be sure they have clean water, and granulated salt free choice, or they won't drink enough water even in hot weather.
:no: The other concern is that going away and leaving a flock of sheep for a week is a pretty good recipe for disaster. We have raised sheep for years, and DH and the kids look forward to vacation week AWAY from here (I'd rather stay home), but even if a neighbor looks in on them once a day, they are vulnerable to so many things. Example: we left to go on vacation for a week, the neighbor boy was to feed and water them each day morning and night, but we still lost 2 to coyotes one night. Even though he borrowed the other neighbor's donkeys to stay with the sheep (brilliant strategy on his part) the next night the coyotes were back and we lost more sheep. A neighbor who doesn't raise sheep, and even novice shepherds like yourself, cannot anticipate all the ways sheep can find to get themselves killed. :no: Sunstroke, worms + heat, dogs, coyotes, getting caught in fence, etc. One thing we have learned is you have to keep a close eye on them all the time - they can get sick or injured, especially in summer, and look a little off one day, and by the next day or two can be past the point of no return.
Not to discourage you from taking off, but livestock raising is a job that requires daily caring for the animals that depend on you. If you have a way to leave them where someone who knows sheep can take care of them, it might mean more peace of mind and less chance of losses. Just yesterday I had to help hubby free a ram lamb who had somehow managed to get himself tangled up, completely upside down, in the fence. He would have died if we hadn't seen him and got him loose. We also had a neighbor watching the place another vacation week (I really hate vacations) only to come back to find our beautiful GP puppy was very ill, and had been for days, getting worse as time went on. The well-meaning but inexperienced neighbor thought the pup was depressed because it missed us, and didn't realize it was sick. It was not his fault, but the pup ended up dying. I do not look forward to this summer's annual vacation week. Wish I could pack up all the livestock and take them along, at least then I wouldn't worry. But the chances of finding an understanding motel which allows flocks of sheep, goats, chickens, and assorted dogs and cats are rather slim.

 

I have seem how "dumb" sheep can be with our lamb, he will go off the graze all alone, far away from the goats who would warn him of danger, and he will walk into the "going to get squished" side of a moving tire.

I think they should be checked several times a day and locked up at night, if you don't have a gardian to live with them.

 

Ditto

 

Then with your situation, I am thinking a simple painted plywood roof on legs would work. If you have high winds a t-post driven in deep and fastened at two of the corners would hold it down.