Ventilation for small porch

[GettingOnWithItAll]

I'm building a small unheated in-fill porch with external dimensions of 2.1m front, 1.2m sides (one a lounge wall and the other my neighbour's porch) and 2.2m height to the tiles at the front. It'll have a pitched roof, composite door and a window with small casement opening above a 0.9m high dwarf wall. The dwarf wall will probably be single skinned with battens, duplex plasterboard and a plaster skim; a double-skinned cavity wall takes an extra chunk off the interior space and I'm wary of having just a single skin even for an unheated porch. It'll be used primarily as a coat and buggy store whilst providing extra insulation to the hall for winter.

The porch is well within the limits to not need planning permission or meet Building regs. I would, though, like to do a good job even if that means extra work and expense.

The porch will be North-facing and in almost permanent shade. I'm getting confused over the best way to ventilate it. I don't want to rely on opening the small casement window. Will a black hole vent in the brickwork be adequate, or should I go complicated with a moisture-controlled electric fan? Where is the best pace for a vent. Will the roof require a vent (I suspect not)?

Any advice gratefully received.