Some Spanish adjectives have a shorter form (they drop their -o) when they precede a masculine singular noun. These adjectives include:

Complete form ----> Short form

alguno              algún
ninguno             ningún
bueno               buen
malo                mal
primero             primer
tercero             tercer
postrero            postrer 

Examples:

Esto es un café bueno. ---> Esto es un buencafé.

Juan es un hombre grande. ---> Juan es un gran hombre .

Remember that the short form is used when it precedes a masculine singular noun. If it follows a masculine singular noun (as it does in the above examples to the left), it preserves its complete form.

The following examples show that for all other nouns the adjective is used in its complete form.

Estos son los primeros días del año. - These are the first days of the year.
No veo ninguna razón para trabajar. - I don't see any reason for working.
Tú siempre tienes malas ideas. - You always have bad ideas.

The adjective grande is generally reduced to its short form before a singular noun of either gender. It is not shortened when it follows a noun or when it is in the plural form. It is also important to note that when it comes before a noun grande means "great," when it follows its noun it means "big."

San Francisco es una gran ciudad. - San Francisco is a great city.
San Francisco es una ciudad grande. - San Francisco is a big city.