Typical thickness of a slab of a condo unit will be about 100 mm or 4 inches. The IIC of that kind of flooring will be about 25. So if your drum set will be giving an SPL of 100 dBA, about 75 dBA will still penetrate. It would help if you place a thick carpet installed wall to wall with a thick underlay. The IIC of something like that would be about 46. Do the math. Now, the floor is not be the only possible place where noise will penetrate. Your walls and ceiling are also culprits. Reinforce the walls and the ceiling with double or even triple gypsum, 12 mm each. Addition of glass fiber inside the wall cavities will increase the STC of your wall and ceiling by another 5 to 6 dB, depending on the thickness of the fuzz. Adding air space would further increase your figures, again depending on the size of the cavity. The only problem is once you do all these, your room will become smaller. Using metal studs instead of wood studs will increase the sound transmission stoppage capability of your walls or ceiling. After all these, you have to contend yourself with decreasing the room gain, by adding absorptive materials as final finish. You can absorb, diffuse or reflect sound. But that will be a bit complicated. Putting thick curtains on certain wall areas walls would help. Trying to find the best combination of curtain and your hard surface wall finish will give you a room that will not be totally damped. (Forget egg trays - no useful abs coef. value, especially foam - very flammable). Experiment. To do it properly, you have to use a bit of computation using Sabine, Fitzroy, or any of those RT60 equations. But that is going a bit far, unless you devote a lot of time and study on them. It is Math and Physics. For now, keep things simple. It is rather complicated to understand sound. Mitigating or stopping it needs your first understanding its properties, characteristics and the necessary methods to tame it. Aside from knowing all these, you need to have extensive practice on it as well. These take years of exposure, study and experience. But if you are truly interested in it, you can probably start now. Go over the net and research on it. Good luck in your endeavour.