Learn Russian: Снаружи здание красивое, а комнаты старые. - Outside the building is beautiful, but the rooms are old.

In Russian, а is used to contrast two things that are different but not contradictory, like comparing the outside of a building to the inside. You use но for an unexpected result or direct contradiction, for example: The building is beautiful, but I do not want to live there.

Could I use на улице instead of снаружи to say 'outside'?

Not in this context. снаружи refers to the physical exterior of an object, like the outside walls of this building. на улице literally means 'on the street' and is used to talk about being outdoors in general or the weather outside.

Why is the word снаружи placed at the very beginning of the sentence?

Russian often puts scene-setting words like location at the beginning of the sentence. By starting with снаружи, the speaker establishes the 'outside' as the topic before describing it, which naturally sets up the contrast with the rooms inside.

Why does красивое end in -ое when здание ends in -е?

здание is a neuter noun, so the adjective describing it must also be in the neuter form. For most adjectives like this one, the standard neuter ending is -ое, regardless of whether the noun itself ends in -о, -е, or -мя.