The building was used most recently as a sale room

The Grade II listed structure was originally built as a Sunday school at the start of the 20th century, but more recently was a saleroom.

It is being marketed with potential for conversion to a one-bedroom house, although it would need a lot of work.

Estate agent Stephen Tudor said it was an example of a type of building which was becoming "increasingly rare".

And planning consultant Mark Roberts said it was characteristic of a specific time in building history.

Beautiful in own way

"These type of buildings are beautiful in their own way, and they are getting increasingly rare because of the materials they were built from," said Mr Tudor.

The Porthmadog example was first built as a Sunday school for the local Tabernacl chapel.

Cadw - who look after Welsh historical monuments - listed the property because of "its special architectural interest as a well-preserved church hall using prefabricated materials, a type once common but now rarely well preserved."

Ken Humphreys, 59, and his twin brother Robert used to attend the Sunday school as young children.

These are structures which are specific to their time Mark Roberts, planning consultant

"There were about 15 of us who attended the Sunday school. I remember it as a simple zinc shed fitted with benches, you could hear everything, and it was particularly noisy when it rained," he said.

Pre-fabricated buildings were seen as a way to build cheaper structures especially for schools, churches and halls, places where people did not spend a lot of time, said planning consultant Mark Roberts from Rhostryfan near Caernarfon.

"These are structures which are specific to their time, when the cost of traditional building materials were too expensive," he said.

An example of a modern way to use "corrugated iron" can be seen on the new hospital building in Porthmadog said Mr Roberts.

"Of course agricultural buildings still use corrugated iron, very simply it's form follows function. They are very simple buildings built for a purpose," Mr Roberts added.