Learn from my experience

If you live in flats and are only replacing some of the windows,
insist, really insist, that the dimensions of the new frame are as
close as possible to the existing - so that the new frames do not
stand out like a sore thumb. I guess that UPVC is structurally much,
much weaker than wood or metal hence the UPVC frame needs to be much,
much thicker to support the glazing units. If they are very much
thicker than the other unchanged units, they will look ridiculous.

Look at a mock-up of the style of the window. Other windows in my
block have a simple mitre between the frame and the glazing unit. My
new windows have some ridiculous extra fillet between the frame and
the glazing that irritates the **** out of me. I am trying to get that
rectified but I don't hold out much hope.

My new windows look clumsy in comparison to others in the block and
only because the previous metal windows were so ghastly (constant
mould, constant paint flaking, constant condensation) am I not going
to take an axe to the new ones.

Clive