HO Railroad HQ 4 Story Add-On View Larger Image Price: $85.00 Quantity: Scale HO Size 11"W x 7.5"D x 5.75"H HO Scale kit features laser cut acrylic with tab and slot construction. HO Scale Add On kit features laser cut acrylic. Add four stories to the Railroad Headquarters Building with this kit. Want to make it taller? Use one or several Add On kits. Kit features laser cut acrylic parts. Tab and slot construction, detailed instructions and photos help with assembly. Download a copy of the HO scale instructions for the Railroad Headquarters building. Related Products HO Railroad Headquarters Price: $245.00 Quantity: HO Railroad HQ 6 Story Add-On Price: $110.00 Quantity: Glue Bottle Price: $4.25 Quantity: