ᐅ Costs for partial vertical extension and flat roof with rooftop terrace – experiences?

Hello,

I have possibly found a suitable property for me and my family.
It is built on a plot measuring 6m x 17.1m (20ft x 56ft), with the long east side adjoining a neighboring building.
Half of the house has an upper floor with a 10° pitched roof, while the northern half has a sloped roof.

To create more living space, I would like to add an extension measuring 9.75m x 6m (32ft x 20ft) on top (room height 2.9m / 9.5ft).
The pitched roof would be removed, and a full flat roof terrace installed with a horizontal roof access and skylight.
The whole extension is to be built using timber frame construction, and the roof should be as energy-efficient as possible.
I plan to do as much of the work myself as possible.

Could an experienced person kindly provide an estimate of the cost for approximately 16m (52ft) of timber frame wall with several windows about 3m (10ft) high,
a 17m x 6m (56ft x 20ft) flat roof with roof terrace, and the demolition of the old roof, done as economically as possible?

Thank you very much.

Very rough sketch only for better understanding.

I would estimate around 200k + X.

nordanney schrieb:

I would estimate around 200k plus extras.

Could you break down the costs a bit?

So far, I’m budgeting approximately €25k (about $27k) for 48sqm (516 sqft) of timber frame wall,
around €40k (about $43k) for 100sqm (1,076 sqft) of flat roof, and €80k (about $86k) for 100sqm (1,076 sqft) of roof terrace,
with own labor included. So more like €150k (about $161k).
Where am I going wrong?

HE-DA-Doppelhaushälfte schrieb:

Where is the mistake?

There is no mistake. These are all estimates.
Are you a builder or tradesperson to know the prices so well? What kind of DIY work is planned?
I generally calculate using square meter prices for living area.

The difference ultimately lies in many details:
- Type and amount of possible DIY work
- Insulation of the roof terrace, type of waterproofing, surface covering, parapet design
- Quality/type of windows
- Shading?
- Electrical system
- Heating, etc., just to name a few key points to inquire about.

Even your term "as energy-efficient as possible" can lead to significant additional costs, depending on what exactly is meant by this.
Your list is too general to be specific, so only a response with general estimates is possible and reasonable.

The huge window on the south-facing facade alone is likely to cost at least five figures, plus shading.