"We have had, as you can see, a very lengthy discussion with President Kibaki... these issues require time to discussed so that an agreement is reached," he said.
A statement released by Kibaki's office said: "During the meeting, the president and prime minister-designate agreed on the way forward in the implementation of the National Accord and Reconciliation 2008."
"At the meeting the two agreed on a 40-ministry cabinet that will be announced this Sunday, 6th of April. The new cabinet will then be sworn in on Saturday 12 April 2008," the statement added.
The formation of a coalition government is key to the implementation of a February deal that ended two months of deadly post-election violence in the east African country.
The agreement, already enshrined in the constitution, was reached in a bid to stem the unrest that flared after the incumbent was accused by his rival and pre-poll frontrunner Odinga of rigging his way to re-election.
The international community also voiced concern over irregularities in the vote counting, but urged both sides to stem violence that has left at least 1,500 dead and hundreds of thousands displaced.
Kibaki had long insisted on a cabinet with 44 ministers, while Odinga demanded 34.