Display what buildings yet need upgrading
A simple button, possible an addition when you click on the builders hut that says or shows "Future/Need-To-Be-Done Upgrades". A small yet semi detailed listing of all towers and buildings that the player needs to still upgrade (When a building is max level for the respective Town Hall it doesn't appear on this screen).
The button: Similiar to when you click on the Barracks and has a "Train Button", except this is an "Upgrades" button with coin or elixir as its image. One simple button with a simple screen pop up showing future upgrade for the current TH level on the left side, and possibly showing the requirements such as coin or elixir on the right hand side.
This would be very helpful to view all upgrades left for my Town Hall instead of clicking on each individual towers to find out if they're max or need upgrading.