Example:-
1st Blue Site (eg:name of street) = 1 house
2nd Blue Site (eg:name of street) = 1 house
3rd Blue Site (eg: name of street) = No house
Buy a house for the 3rd Blue Site then you can buy a second house on any of the the three Blue Sites when you land there the next time, but next time you must buy a house it must be the one that has the least number of houses. When you, at last, have 4 houses on a Site, hey

you can buy your first hotel.
Same goes for Yellow. You can go back and forth. When you have 4 houses on a property you can then buy your first hotel and milk the rent money in.
Who said Monopoly is boring

Go and become rich.
Regards.