Don't do a square route, there's an easier way.
Pick two a/d with ICAO codes that straddle the area you want to brief for, i.e. the area you want to brief for sits in beween them.
Use them as your departure and arrival a/d
Draw a line between them and decide how much either side of this line you want the info for. Set this as your Narrow Route Width.
For example up near the top left of the southern half mil is a microlight site at Otherton, it lies between Cosford and Tatenhill, which are around 20nm apart. set a narrow route width of 10nm and you've defined a 400 square mile box between them.
If there are any aerodromes within the area that you want NOTAM for then set them as alternates.
Fill in the Briefing id as something meaningful, e.g. Local.
Any time you want to use it go to the Briefing Handbook and re-use it, it will be listed under the name you chose.
Mike