Mount EverestG 10

Save this one and Marathon runner for one of the last achievements you do.
I was at around 20-30 percent before finishing the story.

The easiest method is to buy a house with a huge ground outside.
Then build a horizontal wall-line as long as you can, from one end to the other.
Then go to Options, Gameplay Settings, change the "Using tools" option to Toggle. (This prevents holding down RT)
Now place the paint roller on the wall and use the D-pad from left to right (it is faster than using LS), you do luckily NOT NEED PAINT for this!

Toggle the achievement tracker if you like to keep track and just go from left to the right till it pops!