Sur le toit, la gouttière est pleine de feuilles après l’orage.

Yes. Sur le toit means on the roof.

French often puts a place expression at the beginning of the sentence to set the scene, like:

• Sur le toit, ... = On the roof, ...

It is a little like saying:

• As for the roof / Up on the roof, the gutter is full of leaves after the storm.

The comma shows that Sur le toit is an introductory location phrase.

La gouttière means the gutter.

It is feminine in French, so it takes the feminine article la:

• le = masculine the
• la = feminine the
• l’ = the before a vowel sound

So:

• la gouttière = the gutter

Because pleine agrees with la gouttière, which is feminine singular.

The adjective plein / pleine means full:

• masculine singular: plein
• feminine singular: pleine
• masculine plural: pleins
• feminine plural: pleines

Since gouttière is feminine singular:

• la gouttière est pleine = the gutter is full

The expression être plein(e) de means to be full of.

So:

• plein de / pleine de = full of

Examples:

• Le sac est plein de livres. = The bag is full of books.
• La rue est pleine de monde. = The street is full of people.

In your sentence:

• la gouttière est pleine de feuilles = the gutter is full of leaves

After plein de / pleine de, French normally uses de, not des.

So you say:

• plein de feuilles = full of leaves
• plein de neige = full of snow
• plein d’eau = full of water

Even though feuilles is plural, the structure is still plein de + noun.

Also, when de comes before a vowel sound, it becomes d’:

• plein d’eau

Feuilles means leaves.

The singular is:

• une feuille = a leaf / a sheet of paper

The plural is:

• des feuilles = leaves

In this sentence, it clearly means leaves from trees, not sheets of paper.

Après l’orage means after the storm.

Breakdown:

• après = after
• l’orage = the storm

So:

• après l’orage = after the storm

It tells you when the gutter became full of leaves, or when this situation is true.

Because orage begins with a vowel sound.

In French, le or la usually contract to l’ before a vowel or mute h:

• le arbre → l’arbre
• la école → l’école
• le orage → l’orage

So:

• l’orage = the storm

Yes, that is possible, but it means something slightly different in structure.

• Sur le toit, la gouttière est pleine de feuilles après l’orage.
  • starts by setting the scene: On the roof, ...
• La gouttière sur le toit est pleine de feuilles après l’orage.
  • sur le toit now sounds more directly attached to la gouttière, as if specifying the gutter on the roof

Both are grammatical. The original sentence feels more natural if the speaker wants to begin with the location.

French often uses the present tense est where English might use is or understand a recent result from context.

• la gouttière est pleine = the gutter is full

Then après l’orage gives the time context:

• after the storm

So the full idea is:

• After the storm, the gutter is full of leaves

English might sometimes say:

• The gutter is full of leaves after the storm
• or The gutter ended up full of leaves after the storm

French does not need an extra verb here.

It is literally on the roof, but in natural English it can also feel like up on the roof, depending on context.

French sur usually means on:

• sur la table = on the table
• sur le mur = on the wall
• sur le toit = on the roof

In this sentence, up on the roof is a very natural English rendering, even though French just says sur.

A fairly close word-for-word breakdown is:

• Sur le toit = On the roof
• la gouttière = the gutter
• est = is
• pleine de = full of
• feuilles = leaves
• après l’orage = after the storm

So the full sentence is:

• On the roof, the gutter is full of leaves after the storm.

A more natural English version might be:

• After the storm, the gutter on the roof is full of leaves.
• Up on the roof, the gutter is full of leaves after the storm.

A learner would often notice these key points:

1. Introductory place phrase

   • Sur le toit, ... = On the roof, ...

2. Gender

   • la gouttière is feminine

3. Adjective agreement

   • pleine agrees with feminine singular gouttière

4. Common expression

   • être plein(e) de = to be full of

5. Plural noun

   • feuilles = leaves

6. Elision

   • l’orage instead of le orage

7. Time expression

   • après l’orage = after the storm

So although the sentence is not very long, it contains several very common French patterns.