This is a block I created a little over a couple of months ago and it was based on a co-worker's request.
It's basically a 10 sided closed Pline with stretch actions and a field that looks up the area of the object.
Just like a normal pline, if you reduce (or connect) the points, it adjusts and can turn into a 3 sided area block (if that's what you need).
I have a 9 sided, 8 sided etc etc all the way down to 3 sided area block. But the 10 sided one covers all those needs. And I also have it in Metric and Unitless, though they are not completely finished yet - more because I'm lazy than because it is hard.
And when you need a new one, you just insert a new copy of the block and you're good to go again!