Poor Boy Fabry–Pérot interferometer?

I want to build a Fabry–Pérot interferometer in order to study and understand the equipment and technology.

Fabry–Pérot interferometer Wiki

It is also an excuse to buy my first "Lab Laser".

I intend to use this device to attempt to measure gravity. (proximity or even orientation to a large object "mountain, peak, valley" should produce different repeatable results)

So I think I have found a candidate HeNe for this project.

Fleaybay 20mW HeNe