Correction:

1. It was raining today.

Correction : Aj-ke brish-ti ho-ye-che. (Ajke - today; Brishti - rain; Hoyeche - to take place)  

2. It stopped raining now.

Correction: Akhon brish-ti tha-meye-che. (Akhon - Now; Thhe-mee-che - stopped) 

3. Ajke (it was warmer than yesterday) khun garam ki ayer???.

Correction: Ajke goto-kal theke gorom beshi chilo. (Goto-kal - yesterday; Theke - than/from; Beshi - more; Chilo - was)
 
4. Aami bahire gieche y aik sandwhich kenechi.

Correction: Ami bahi-re giye-chi ebong ekta sandwich kine-chi. (Aami - I; Bahi-re - outdoor; Giye-chi - went; Ebong - and; Ekta - one; Kine-chi - bought)

 
5. Aami shop kayechi. Khub bhalo chilo.

Correction: Aami puro-ta kheye-chi. Khub bhalo chilo. (Puro-ta - whole; kheye-chi - ate; Khub - very; Bhalo - good; Chilo - was)

6. It has onions and vegetable. Pez chilo ar shobji.

Correction: Eta-te pe-aj ebong shob-ji aa-che. It's the translation to "It has onions and vegetable." (Eta - it; Pe-aj - onion; Shob-ji - vegetables; Aa-che - has)

N.B. You can use chilo if you want to use had.

i.e. It had onions and vegetables. Translation - Eta-te pe-aj ebong shob-ji chi-lo. (Chi-lo - had)

7. Soon it may snow. ????

Correction: Shigh-roi tushar por-be. (Shigh-roi - soon; Tushar - snow; Por-be - fall)

8. Maybe I will leave soon Hayeto ami cholo jabo. Beshi thanda acche.

Correction: Hoy-to aami cho-lay jabo. (Hoy-to - maybe; Chole jabo - leave)

9. Ami anek thanda bhalo lage na. Ami garam Weather? bhalo lage.

Correction: Amar thanda bhalo lage na. (Amar - mine)

Or you can write : Aami thanda po-chon-dow kori-na. (Thanda - cold; Po-chon-dow - like; Kori - do; Na - not; Kori-na - don't)

Amar gorom weather bhalo lage.

Or you can write : Aami gorom weather po-chon-dow kori.