I wrote the sentences using as and my own ideas. Are these natural?

-English grammar in use
Unit 116 As
116.5
1. I saw you as I was at the cafe.
2. It started to rain just as I leave home.
3. As I didn't have enough money for a taxi, I went to walk.
4. Just as I took the picture, it was rain.

Question

I wrote the sentences using as and my own ideas. Are these natural?

-English grammar in use
Unit 116 As
116.5
1. I saw you as I was at the cafe.
2. It started to rain just as I leave home.
3. As I didn't have enough money for a taxi, I went to walk.
4. Just as I took the picture, it was rain.

Answer

1. I saw you as I was COMING OUT OF the cafe. (these happened at the same time: you could however say 'I saw you when I was at the cafe'.)
2. It started to rain just as I WAS LEAVING THE HOUSE. (or ...'I LEFT HOME')
3. As I didn't have enough money for a taxi, I DECIDED to walk.
4. Just as I took the picture, it BEGAN TO rain.

I have this book and have looked at the chapter.
Number 3 does make sense as you had it, but it would imply that you INTENDED to walk, but perhaps ended up not doing so.

Answer

Here are your sentences revised for naturalness and correctness:
1. I saw you as I was at the cafe.
    * This is mostly correct, but it would be more natural to say: "I saw you while I was at the cafe."

2. It started to rain just as I left home.
    * "Leave" should be changed to "left" to match the past tense.

3. As I didn't have enough money for a taxi, I decided to walk.
    * "Went to walk" should be changed to "decided to walk" for clarity.

4. Just as I took the picture, it started to rain.
    * "It was rain" should be changed to "it started to rain" for correctness and clarity.

So the corrected sentences are:
1. I saw you while I was at the cafe.

2. It started to rain just as I left home.

3. As I didn't have enough money for a taxi, I decided to walk.

4. Just as I took the picture, it started to rain.

Answer

Have you got the "red cover" English in Use
or
the "violet cover" English in Use?

Answer

1. I saw you when I was at the cafe. [means that I saw you while I was at the cafe]
2. It started to rain just as I was leaving home. [since "started" is past tense, it can't be "leave." It has to be "was leaving"]
3. Since I didn't have enough money for a taxi, I walked. [you can use "as" instead of "since" only if you reverse the clause order. An example would be "I chose to walk, as I didn't have enough money for a taxi."
4. Just as I took the picture, it started raining. [it started at the moment you took the picture] OR "As I took the picture, it was raining." [it had already been raining, and you chose to take a picture]