Wall ovens are usually installed into a full height cabinet. Clearance, ventilation and wiring requirements are specified by the manufacturer. Most do not require supplemental ventilation, but may require a small hole in the bottom of the cabinet to provide some minimal convective movement. All wall ovens are well insulated with fans that circulate air through a shell so inner heat is ejected back into the kitchen, not the enclosure. Don't sweat the venting, shop your ovens and obtain a copy of installation instructions and rough-in requirements for that model. Then go shop a cabinet or have one built.