If he's looking for a chill place with great weed, tell him to go to Up in smoke on soi honey. Nice place and can smoke there, but just like all the other dispensaries prices are a rip-off at 6-700 baht a gram or so, also whichever weed he buys, they will roll it up for free.
For a tourist, first time traveling, who cares about the price.
https://www.up-in-smoke.org/