Not sure you can really at least easily or at all - as if you consider how the lifts are constructed and recognised by the engine. They in fact normally stop by default when they get to the lift top section of the Lift segment which is placed in a level.
This they do automatically as lift segments are recognised internally by the engine as objects the lift entity should start or stop at. This is all hidden from the end user.
I guess there may be ways to control the stop or start positions of lift platforms or other entities - though it wont be easy as it invloves in this instance overiding FPSC defaults or trickery and workaround to beat the daylights out of its stubborn restrictions.
You could of course try the path method and use the waypoint commands "start", "stop" and "reverse" in a script to try and give control to the user.
Also study of how the follownorotate script works and is set up may be of some help.
Unfortunately it may require some hard graft to find a workable solution via scripting - as far as I know there is no way by default for the user to use any feature, function or entity object to help them stop a platform moving in the vertical direction.
Control of the lifts and such as with many other things has been removed from user influence by TGC - fair enough perhaps as they basically and probably dont want users messing with them and then complaining they dont work properly I guess. Its click and play and anything else is generally hard work in achieving.
I am sure some of the knowledgeable scripters here may have a solution or someone may already have done this and will post here if they read this.
At least you can fly upwards and look back down and take those interesting downward view screen shots - so its a worthwhile learning curve doing anything in FPSC.
I am not sure if one could make say a copy of a lift top segment (and its associated files) - then make it transparent and place it somewhere above where you want the platform to stop. I guess such a top need not be a whole segment like room but could possibly be a smaller entity . x file model so would not take up much room and get in the way. Some trickery might just work - though FPSC is fussy if not clever about these things.