My friend and I just started in vex this school year and have tried to look everywhere for videos or pictures on how to build a telescopic lift. However, we have had no such luck. I would greatly appreciate it if someone could help us. 
Usually I have seen it being called an elevator lift in Vex, maybe you would have better luck searching with those terms. jpearman’s Triple lift thread has some very good and detailed photos on it that could help you.
From my experience this kind of lift isn’t the simplest nor easiest to perfect and get working well, especially if you are new to Vex or robotics.
EDIT: Before you build or start anything it is good to initiate a design process, analyse the game, establish goals, brain storm so you can be sure that what you are building is what will best accomplish most of your goals.
The linked thread is one variation of an elevator lift, and as is discussed on the thread, there are many advantages and disadvantage to that variation and other variations the lift. You should use this as a starter and research widely but crucially plan lots, before you build your robot.