My answer assumes that you're talking about the rails and stiles for the drawer fronts and drawers, not the cabinet boxes (face frames). It's fairly common to do a single, shallow drawer front as a slab in a Shaker kitchen. Then your rails and stiles are consistent everywhere else, and the slim top drawer doesn't look crowded. Here's an example:

https://www.houzz.com/photos/mill-valley-classic-cottage-victorian-kitchen-san-francisco-phvw-vp~1357985 

Our standard stiles & rails are 2 1/2". On the top drawer, rails are 1 1/2".

Merrimak · More Info

Thanks @salex. Yes I've seen that the top drawer is slab in many cases. I was just trying to avoid that look (personal preference). Thanks @Creative Design Cabinetry - this looks more like I was trying to achieve and your dimensions aren't far off from what I have. From what I can tell you have some drawers that are wide (hard to tell from picture) and the thin rails don't look out of proportion which is good.

My rails and stiles are 2 3/8". On top drawer the rails are 1 5/8".

My top drawer is 6 1/4" high.

To avoid the changes in stile/rail width on drawers, I tend to do the Shaker fronts for the cabinet doors, only, and then do slab drawers. In the pics below for a kitchen recently completed, the doors have a center stile to give it a Craftsman look, but the same principle applies to plain Shaker:

Bernal Heights Sustainable Kitchen · More Info

Bernal Heights Sustainable Kitchen · More Info