Want to build a cowboy cirt shotgun build but I don't know where to start any help will a great help

Look up a list of perks, then take all the perks that improve your chance of scoring critical hits (like Finesse) and perks that improve shotgun effectiveness (like Shotgun Surgeon). Regarding your playstyle, since you are using a CQC weapon, I would recommend a high Agility stat and light armour to increase speed, so you can close the gap with enemies easier.

If you're going for cowboy, you need a Lever-Action Shotgun, Shotgun Surgeon, and And Stay Back at a minimum.

Im using these on my current character. Super powerful. Just got the riot shotgun too. Haven't tried against a bunch of deathclaws yet though.

Riot Shotgun being the best weapon in the class, you don't need Cowboy.