Martin, congratulations to you both on the birth of your son.
I went down the 'make your own units' road. I went for MFC, which I bought through a local timber merchant, cost about £22/ sheet (8'x4'). I planned the layout and worked out the sizes of each part for the units. I used a program called Cutlist to optimise the layout for cutting...it cost about the same as one sheet of MFC, so well worth it. I got the whole kitchen out of 10 sheets (I had guestimated nearer 20 sheets) so not too expensive for materials. I have made frame and panel doors out of MDF and painted to suit the boss.
The downside...MFC is a pig to work with. Even with good tools it chips as soon as you look at it and the tools blunt quickly. It also takes longer than you estimate to build even one unit. If, like me you are short on time (and with a new baby you will be) and only get a Saturday or Sunday to work on the project, you may only get one unit or door made in a session.
I know you can get pre-edged MFC that is 570 mm wide, the depth of a base unit side, which makes it a bit easier and quicker but probably more expensive. All-in-all I would probably buy ready made units if I were to do it again, because it quickly goes from being fun to being a chore especially if you get questions from SWMBO as to why it is taking so long to get this 'simple' job done.