I have just made some wardrobe doors for my in laws using MDF panels. To make it easy the doors were a fairly standard size ie. 1800 x 550 mm. I got B&Q to cut the MDF up for me, remember they only cut to + or - 3mm so get it all cut at the same time. The panel size is 9mm thick, then get the edge rails cut to 70mm wide, the bottom rail cut to 70mm wide, the middle and top rails were 120mm wide also out of 9mm thick MDF. Lay the edge rails on top of the panel on each side, mark off and cut to length the bottom, middle and top rails to fit between the side rails and then router over all the inside edges with a small detail cutter. The top rail had a radius on it to give an arch top. Then use another cutter to detail the outside edges. Glue and pin the rails to the panel and clamp up. Sand the door and give it two coats of primer, sanding between coats, then undercoat and gloss/satinwood with a roller. The end result is a top quality looking door at a fraction of the cost of a shop bought one. 
