Take in the West coast of Scotland if you can. A fuel stop North (Kirkbride?) enroute to stay at Glenforsa. Next day top up in Oban and head up to see the Cullins on Skye and then head over to land at New Hall Mains North of Inverness. Fuel at Inverness the next morning and night stop at any of Perth/Dundee/Cumbernauld depending on your range. Day four south to home.
I admit those legs might be a bit long for a Cessna 150 but if the weather's suitable it'll be a trip worth doing.