.... I agree with sending out the plans but I do not think that it is a simple as sending out the plans as they can be priced / intrepreted in so many different ways and I am struggling on how to approach this.
You're dead right. I've seen a contract lost because one builder used a QS to price, whilst another did a calc himself for actual, rather than 'book' costs. The difference in in the house came to 160k. And no, you've no comeback with the QS on it, either. I'm not enamoured by the QS work I've seen.
The problem with sending out plans is, as you've said, there's no spec. So write up something yourself, as a starting point, from a common-sense point of view, and at least get the pricing in the same manner. A one-line quote from a builder with 'to build your house € XXX,XXX is pretty much useless. Those quotes always smack to me of a guy who threw a per-sq-ft price at it, and hoped for the best. You want someone to have earnestly sat down and calculated the actual cost, for you.
Quotes should be at least as detailed as your RFQ - Request For Quote. The more info you give, the more comprehensive, and accurate, the quote. And don't dismiss the more expensive 'looking' one. Check what's actually included, or not, to compare. You'd be surprised how many of the 'cheap quotes' work out to be nothing of the kind........
In general, though, if you can, and are in a position to, yes, it's a great time to build.
Make it fun !