Atarashii kamera wo katta.

Onrain de camera wo katta. (onrain de atarashii kamero wo katta.)
Kore wa watashi ga ano toki, gajetto wo kattakau(use present dict. form) no wa hajimetedesu.
watashi wa 15-sai no node, watashi wa kono kamera wo matte iru.
Sore wa, 3-nen ga tachimashitatatta.
shashin wo benkyō shitainode, watashi wa kamera wo katta.
Watashi wa idaina shashin-ka ni naritai.

stick to informal.. :)

onrain de atarashii kamera wo katta.

ano toki, gajetto wo kau no wa hajimete.

watashi wa 15 sai node, kono kamera wo matte iru.

3 nen tatta. 

shashin wo benkyou shitainode, kamera wo katta.

watashii wa idaina shashinka ni naritai.

I hope this helps..