We’ve seen the five-door versions VW Up! and Skoda Citigo, it was only a matter of time until a pair of extra doors was added to the Seat Mii as well.
This "even more versatile" version Seat Mii which will be launched in early summer 2012 comes with a slightly lower roof line when compared to the two-door model, while the engine remains the same: a 1.0-litre 3-cylinder petrol unit available in two output levels, one with 60 HP and the other rated at 75 HP.
If paired with Seat’s Ecomotive technology, which means the car also comes with Start Stop, the 2012 Mii five-door is expected to return 4.1-litres of fuel per 100 Km and emit 96 grams of CO2 per Km, if we are talking about the 60 HP (44 kW) version or 4.2 litres per 100 Km and 98 g/km for the 75 HP (55 kW) version.
James Muir, President of SEAT, S.A. said "With its distinctive SEAT identity, its youthful design and its high
quality standards, the five-door Mii in particular is set to capture a
significant share of the sub-compact segment. This makes the Mii an
important factor in our corporate strategy. The Mii marks the start of
the most extensive model offensive ever undertaken by SEAT." 
The 2012 Seat Mii five-door will be offered with the City Safety Assist which can automatically apply the brakes at speeds below 30 Km/h in order to prevent a possible impact, plus the car comes with the SEAT Portable System which includes a 5-inch touchscreen that can be removed for mobile use.
Customers who will chose the five-door Mii will also have the option of equipping their car with a panoramic glass roof.

Source: Seat