the highest returns on real estate are found within hotel setups. Hotels are very dependent on location. The best way is to get the best location near a major rad then put up a hotel. You can rent out the hotel to someone or run it yourself.
With 50m, the best is to buy a 0.5 acre for 20m near JKIA,Msa rd, Athiriver, mlolongo e.t.c then build a 25 room 1000m2 hotel for 30m. This will give you 25 x2000 x 30 =1.5m per month. This will pay back in 3 years.
As Iron Sharpens Iron, So one Man Sharpens Another.