How to build a high sensitivity EEG headset for continual monitoring? After having a conversation with a couple of the more popular "consumer" level EEG makers such as Versus, I have found that their monitoring abilities are either limited or altogether absent.  The devices utility, while cool from a 3rd party controlled training standpoint, is neutered when it comes to just getting raw data and plotting it out in a manner that allows one to make their own interpretations and calls.

I would like to build my own device that can monitor from the very low &lt; 0.5 hz all the way up to at least 200 hz.  My goal is to feed that into my own software in order to keep a running graph for analysis, etc.

How would one go about building an EEG that has this level of sensitivity?
There are a few commercial EEG makers that do allow monitoring of raw EEG data. For instance, I know the Muse headband and OpenBCI allow you to do this with little trouble. These both support sampling rates up to 250 Hz. (The OpenBCI in principle could have a higher sampling rate, but i don't know anyone who has done this.)

The Emotiv EPOC also has an option to get raw EEG data. You have to pay more for the research version of the SDK to get the data officially. However, someone has reverse engineered their protocol, so you can access the raw data that way. This has a sampling rate of up to 128 Hz.

That said, if you still want to build your own EEG, OpenBCI has documented all of their plans, so a good start would be to replicate their product. 

There is also the older, but still useful, OpenEEG project, which also has open plans for an EEG device.