Last month I let a garage that I own in Prague 5.
I managed to get a rent of 2,500 CZK / mth, with a years contract.
Given that a typical garage space costs around 300-400,000 CZK, this gives an approximate rental yield of 7.
5 - 10%.
This is far higher than the yield from an apartment in Prague (typically around 5% currently).
I'm not suggesting going round buying a lot of parking spaces in Prague (though it might be good idea) as they are a little more difficult to rent than apartments and demand varies from location to location, building to building.
Also there is a lot of hassle involved in renting each space for a small amount of money, so its not the most scalable strategy (unless you buy a parking building).
That said with the growth of car ownership in Central and Eastern Europe the trend will be for increased demand and higher prices of parking spaces, especially in the major cities, such as Prague.
Overall, I would always recommend buying a car parking / garage space when buying an off-plan apartment in Prague.
Increasingly, more and more tenants ask for them and they certainly help resell an apartment more quickly.
I'll certainly be buying more garage spaces in Prague, especially as there are plans to expand the current parking restrictions in Prague 1 (and parts of Prague 2 & 7) to other districts of Prague.
Demand for garage spaces is only going to increase.
Typical garage spaces in Prague rent for 1,500 - 5,000 CZK/mth, and cost from 300 - 600,000 CZK.