Every President has a monument-his library and a memorial-his headstone. If you are talking about something along the lines of Lincoln’s or Washington’s in DC, well that won’t be up to us, it will be up to future historians decades after Obamas legacy plays out and political opponents are long gone. We are unlikely in future to go toward imposing, iconic statues or symbols, those are out of fashion.
Look at the FDR memorial near the mall, It is more a park/museum than a glorification of FDR. His statue is at ground level and just 10 feet tall. Posed in a wheelchair Roosevelt looks very accessible instead of towering over and looking down on the capitol.