I've had this problem...couple ways you can go depending on how neurotic you wanna get with detail. Easiest fix is to place those stair symbols as you have them without resizing and then apply a transparent shadow layer over them. So, create a new sheet and load up the transparency symbols (Bitmaps -> Tiles -> Transparency). You'll see that you have varying shades of grey. Pop in those varying shades with the lightest on the 2nd floor and darkest at the foot of the stairs.
If you wanna get into more detail - those stair symbols you have already have a shadow created for them. So putting one next to the other may look a little odd. To get around that, you could individually draw each step and put it on its own sheet and add a drop shadow effect to the sheet (messing with the sun direction to make sure the shadow faces the stair below it). I've done this for maps that have a few steps - never as many as you have here.
Alternatively, you create a new symbol in photoshop and drop it in. I'm unfortunately not very good at that...
Hope that helps.