VEGETABLE BEGINNER

MORNING ALL,HAVE JUST REGISTERED ONTO SITE SO I HOPE THIS WORKS.
 MADE A SNAP DECISION IN SUMMER TO TRY VEGGIES NEXT YEAR.HAVE CLEARED A SMALL SECTION OF GARDEN AND PLANTED A CONFERENCE PEAR IN THE GROUND AND A VICTORIA PLUM AND BRAEBURN APPLE IN LARGE POTS AS A START.
 MY QUESTION IS,SHOULD I CONSTRUCT THE RAISED BEDS AND FILL THEM OR WAIT UNTIL THE END OF THE WINTER SO ANY GOODNESS IS NOT WASHED THROUGH.WHAT SHOULD I USE TO FILL THE BEDS,ALL TOPSOIL OR MIX OF TOPSOIL AND COMPOST.WHAT RATIO IF A MIX AND WOULD GARDEN CENTRE GENERAL PURPOSE COMPOST BE OKAY.
 AM USING RAISED BEDS BECAUSE OF HEAVY CLAY IN GARDEN,SO PLANT ROOTS WILL SIT ABOVE IT.WHAT DEPTH WOULD BEDS NEED TO BE,AS AREA AVAILABLE IS QUITE SMALL WE WILL ONLY GROW SPECIFIC FAVOURITES.PEAS,FRENCH BEANS,SWEETCORN,CARROTS AND COURGETTES,WITH PEPPERS AND MELONS IN THE LITTLE GREENHOUSE.
 SORRY THIS IS LONG-WINDED AND I HAVE PROBABLY FORGOTTEN LOADS OF STUFF TO ASK BUT WILL RETURN WITH MORE IF THAT IS OKAY,
MANY THANKS,HOPING FOR LOTS OF HELP,BOB STEPHENS.

Hi Bob and welcome! I would probably build the raise beds and fill them early spring. Good topsoil and well-rotted compost should be they way to go. Mix it until you get a good crumbly tilth that should hold together to retain moisture. I suppose the ratios depend on the quality of soil/compost you use.
 
If you are putting the beds on top of thesoil you already have I would suggest you break up the soil first with a fork so if the plants need to get their roots down then they can.

Personally I would go for at least 8 inches deep. Garden centre compost would be good but a little expensive. See if your council has a green sceme, whereby you can purchase compost in bulk. Failing that bulk spent mushroom compost would be ok too! Now would be a good time to get yourself a compost bin....either build from old pallets etc., (which we love!!) or a bought one. You can then put all your garden waste (not perennial weeds or huge branches) and kitchen waste, together with old newspaper and cardboard and that should give you a good start!  

ps Capital letters imply that you are SHOUTING!!!