Jason,

I published an article about the ARLX 1-2000 series refrigerator cars in Railway Prototype Cyclopedia Volume 21. It included overhead photos and ACF drawings that depict the "depressed twin-panel roof" used on these cars. A roof using the same panel design was also on some ACF box cars published in RP CYC Volume 26. 

You're correct about the roof sheets having parallel corrugations. They were somewhat similar to, but different than, some box cars built by Depatch Shops and also on some Milwaukee Road rib-side box cars. The main difference is the area between the twin corrugations in which there is a tapered middle section that's difficult to describe. At a point near the edge of the roof, the middle section is slightly higher than the adjacent raised corrugations, and from there the middle section gradually tapers to its lowest point at the car center line under the running board.

RP CYC Volume 21 is sold out at the publisher but may be available from a dealer. Volume 26 is currently available. 

Regards,

Ed Hawkins