Hi I am getting this gaming pc http://pcpartpicker.com/p/8PVrRB and I am wondering if I should save some more money and get 16gb of ram or I get it when my computer starts getting sluggish
Save your money, 8GB is fine, certainly not necessary to have 16GB right away - but then again if you have the money available and don't want to spend more in the future you could just get the extra 8GB.
8GB will be enough for a while, modern games + OS get to use around 6GB so you have enough RAM free for other stuff while gaming like browsing and such.