With the progression of novel design, material and manufacturing technologies, the wind energy industry has successfully produced larger and larger wind turbine rotor blades while driving down the levelized cost of energy (LCOE). Though the benefits of larger turbine blades are appealing, larger blades are prone to instabilities due to their long and slender nature, and one of the concerning aero-elastic instabilities of these blades is classical flutter. In this work we assess classical flutter prediction tools for predicting flutter speeds in the design of large blades. Flutter predictions are benchmarked against predictions of previous studies. Then, we turn to the main focus of the study, which is design to mitigate flutter. Trends in flutter speeds and flutter mode shapes are examined for a series of 100-meter blade designs. Then, a sensitivity study is performed to assess the impacts of blade design choices (e.g. materials choice and material placement) on flutter speed in a redesign study of a lightweight 100-meter blade with small flutter margin. A new design is developed to demonstrate the ability to increase the flutter speed while reducing blade mass through structural design.