thanks so much for the advice,
im going to buy the kit myself but am clueless about where to start.
do i need a particular model of 105? etc etc i mean for the frame size etc?
Mekk 4g sl primo full carbon frame size 56cm
No, the groupset is one size.
Whatever you buy will fit your frame.
A full group set will contain.
Cranks, Cassette, Brakes (front & rear) derailleur mechs (front & rear), STI Leversx2 (Brake/gears), cables and bottom bracket. (I think I have remembered everything).
Has your frame bolts for a braze on deraillieur or does it take a band on?
You need to decide if you want a triple or double groupset.
Also if you want standard gearing or compact gearing
Have you the tools to do the job? Most of the above can be set up on the bike with a set of Allan Keys and a set of Phillip's Screwdrivers)
For the Bottom Bracket though you will need a BB tool.
You will also need to buy a saddle, Handlebars, seatpost, seatpost clamp, pedals, bar tape, wheels (tyres and inners) and Quick Release levers.
(I guess the frame came with forks and headset)
Some of the best prices for 105 groupsets are from Merlin Cycles (Google for their website).
You Tube is your friend at how to fit components to a frame.
It may also be worth your while getting a book on bike maintenance. Something like Zinn & The Art Of Road Bike Maintenance.