For just day hiking, the bothy sounds good, though i haven't used one so i couldn't say for sure. If you get stuck out there for some reason, a bothy doesn't seem like it would be very nice to sleep in overnight– I would imagine a lot of condensation would tend to build up unless it was well vented (some of the higher end ones do have vents).
Lately i've been toying with the idea of making a simple Tyvek Tube tent. I recently bought some Tyvek material 9 feet wide X 8 feet. It was 1.75 per foot at 9 feet wide (so total cost me about 15 dollars plus shipping). Tyvek is fairly durable for being so cheap, fairly water resistant, and apparently even breathes a little which is an added bonus. Personally, i'm going to give it a DWR treatment of some kind to improve the water resistance. Probably a soak kind. I'm going to cut off a foot, making it 7 feet long, fold it in half (double up the 9 foot part, making a flat tube 4.5 feet wide), glue and tape it together.
Attach some loops to the outside bottom "corners" for stakes, run a cord through the middle (or attach loops to the end to keep it more stretched out and taut), and it's quicker than setting up a tarp, plus you have the groundsheet already.
I have a homemade very breathable (the material is like a light weight powershield type material), but very water resistant bivy i can use it with for extreme rain and/or cold situations.
Downside is i don't know how that shape would hold up in more severe wind, not too mention you could get a severe wind tunnel effect depending or driving rain would get in fairly easily at the head and foot areas. It would be easy enough to add some flaps to the two outside openings to help with that though.