Enlarge the garden terrace directly in a new building?

What is the maximum permissible floor area ratio. It can be found in the development plan.

What is the floor area ratio of the current planning.

Then you compare both numbers and see to what extent the floor area ratio is already utilized.

I have a floor area ratio of 0.3
Plot approx. 315 sqm
I get a terrace 4.20 x 1.80...
I am not allowed more.

Edit: it's about a semi-detached house.

Facts! What are the facts? How much floor area ratio is possible, how much is used?

Or should we wait about 1 year first

That is better. What you are planning may not be legitimate (floor area ratio)

The plot is 400sqm, should actually fit in terms of area, or are there problems in NRW?

You cannot say that superficially or generally.

Thank you for your answers

Floor area ratio = Floor area ratio? then it is 0.4

House + garage definitely count 100%

For the garage driveway and the access path from the house, it depends on the stones how many sqm are counted towards the floor area ratio, whether only e.g. 50% (I have to check later which stones are used, but they should be permeable concrete stones)

The garden terrace also counts 100% towards the floor area ratio?

The garden house probably counts towards it too, right?

Without a development plan and the statute related to it, no precise statement can be made. Generally, § 19 of the Land Use Ordinance applies. However, this is dispositive law and can be deviated from by provisions in the development plan or the statute related to it. For a precise statement, you would have to provide all plans including house planning, development plan, statute, and outdoor facilities.

Does the garden terrace also count 100% towards the floor area ratio?

Yes, generally yes.
For garden houses or garages or additional paving, the development plan must have a provision.