The landmark ONE Subiaco tower has reached its highest point of construction at the 23rd floor, as the developer reveals two more residential high-rises will be launched in the western suburbs next year.

The construction milestone coincides with the sale of 95 per cent of the apartments in the $300 million development.

This includes a penthouse, which sold for $19.3 million. The unnamed buyer also spent $3.7million on another apartment, taking his total investment to $23 million.

Blackburne Development Group managing director Paul Blackburne, who is also behind The Grove development on Stirling Highway, said two similar developments would be launched in the western suburbs in 2022.

Mr Blackburne, pictured, would not reveal the location but said they would be of similar size to the Subiaco and Stirling Highway developments.

He said those who purchased at ONE Subiaco had beat construction price rises, which have jumped about 20 per cent in the past year. He said his development company had signed a set-price contract with builder Multiplex to ensure it was not affected by changing costs.

But while unit prices remained stagnant, values have jumped.

Mr Blackburne said one apartment was recently returned to market at a 20 per cent premium compared with the amount paid by the initial buyer, and sold within a week.

It is understood it is the only apartment that has been returned to market. More than 500 residents will start moving into the 237 apartments across three buildings at the end of 2022. The ground-level market pavilion will include 12 hospitality, food and retail outlets.

The market pavilion, laneways and public spaces are expected to attract up to 5000 visitors every weekend.

Two of the ONE Subiaco buildings — the five-floor Rokeby building and the 23-level Seddon building — have reached full height.

Views from the top level extend to Rottnest Island, the CBD skyline and to the Perth Hills.

The eight-level Roberts building will hit its construction peak soon.