extension on top flat roof extension

[jonnyp1]

I have a flat roof extension area approx 9m by 9m, i want to knock out the internal walls to produce one open plan living area, and build up one half second storey with bedroom and ensuite, and have double height in other area. The front wants to have as much glass as possible, i intend to have t approx 4m glass doors lower opening onto patio. Above one side the bedromm would be 4m glass door opening onto 1 m balcony, the other side would be set back (to provide larger balcony) over the double height, with 4 m doors then going into a 2m gallery suspended, with 2m suspended walkway to stairs.
I am trying to work out approx costs before get her excited.

I believe the foundations were dug with going up in mind, i would raise the existing outer block rendered side wall 3m with flat roof on of 9m by 9m, the back wall (opposite the glass door side) the half with the bedroom suite would be new block wall 6m by 4.5 be , the other half has an existing block wall which i would want to put in unopening glass as big as possible 4.5 m by 2.5m.
I would need to move out side drain and bit under man hole.

I can work out the price for new kitchens flooring, bathrooms etc, and planning architects etc. What i dont know how to do is budgetary price the outside walls approx 60 sq metres, the size and price of rsjs to support the suspended room (9m run) the rsj to support the glass doors 9m on ground floor (4.5m upstairs supported by the 9m supporting the suspended room, the internal wall (timber frame) on the rsj for the suspended bedroom suite, the rsj or timber over fixed glass other side, the size of joists spanning 4.5m, and best way to fix second floor extension roof into existing house.

I am sure this is all to much and not explained properly but any advice good news. Ive talked to some architects who all seems to expect it to cost beween 100k and 200k for whole project which seems crazy to me.
cheers jon

 

[^woody^]

It's still a general £1000/m2 for a second story in traditional build. Your glass structure and that other non standard work will be more than this, but as it's bespoke, you can't generalised in the price and need quotes.

Check that your council allows flat roofs at first floor level. Many don't.

 

[stuart45]

Grand a m2 is really cheap round here now. More like 1.5 to start.

 

[noseall]

A two storey fella I'm building at the mo' is coming in at aboot £900 p/m². It is as simple an extension as you can get i.e. a gable end extended with a modest 30° truss rafter roof, zero drainage, manageable sized openings etc.
I have one on my desk waiting to be quoted and the detailing is suggesting something in the region of £1700 p/m²

 

[jonnyp1]

thanks for replies, i think mine will be a bit of both existing foot print, existing half walls single storey (i believe footings ok), reuseale windows, internal doors radiators, etc, but big chunks of glass and i expect need for some steel.

cheers jon