What would be the best possible itinerary to obtain a 6-month multiple-entry schengen visa?
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With Schengen C visa, you can stay for a maximum of 90 days out of every 180 days. That maximum applies regardless of the number of visa or the countries which issue them, and individual visa may specifiy a shorter duration and validity.
It is a very bad idea to lie (those ghost bookings you mentioned). If that is found out, your credibility on this and future applications will be damaged.
Generally, multiple-entry visa are given to applicants with a history of single-entry visa, or when a single trip takes the applicant into and out of Schengen several times (like a trip to France, the UK, and Italy in that order).
As an UK resident, you may be seen as a low-risk visitor, but the general principle still applies.