Static electricity should be kept as far from an Arduino board as possible.
In the instructables a fet is used (2N3819), but a fet might be destroyed by touching the gate.
So I would not recommend that circuit.
Here is a similar project, also not recommended.
This is an ion detector, a similar project:
I have made such a thing with tree transistors in a row. I had two rows, one with NPN transistors and one with PNP transistors. It was working, but not very well. It picked up the 50Hz of the mains 230V lines. And I had to move it around to detect some static electricity. As if I was collecting ions in the air.
I found a picture of it:
Why do you want to make an electrometer ? For a special purpose ? Should it be accurate ?