Creating multiple Drop downs menus that are variable

Hi Please assist, I want to create a drop down list that has a range of options e.g A1 to A5 would have a,b,c,d,e. i want to reference Columns B1 to B5 to be able to only select certain item from a second drop down list. So in A1 i select B. my only options for B1 would be fat, thin. but if i selected C in A1 my option would be Tall, round.

I hope this makes sense.