By designing are you talking code or graphics? You can find (usable) graphic examples here:
https://opengameart.org/art-search-advanced?keys=gui&title=&field_art_tags_tid_op=or&field_art_tags_tid=&name=&field_art_type_tid[]=9&field_art_type_tid[]=10&field_art_type_tid[]=7273&field_art_type_tid[]=14&field_art_type_tid[]=12&field_art_type_tid[]=13&field_art_type_tid[]=11&field_art_licenses_tid[]=2&field_art_licenses_tid[]=3&field_art_licenses_tid[]=6&field_art_licenses_tid[]=5&field_art_licenses_tid[]=10310&field_art_licenses_tid[]=4&field_art_licenses_tid[]=8&field_art_licenses_tid[]=7&sort_by=score&sort_order=DESC&items_per_page=24&Collection=
https://opengameart.org/art-search-advanced?keys=inventory&title=&field_art_tags_tid_op=or&field_art_tags_tid=&name=&field_art_type_tid[]=9&field_art_type_tid[]=10&field_art_type_tid[]=7273&field_art_type_tid[]=14&field_art_type_tid[]=12&field_art_type_tid[]=13&field_art_type_tid[]=11&field_art_licenses_tid[]=2&field_art_licenses_tid[]=3&field_art_licenses_tid[]=6&field_art_licenses_tid[]=5&field_art_licenses_tid[]=10310&field_art_licenses_tid[]=4&field_art_licenses_tid[]=8&field_art_licenses_tid[]=7&sort_by=score&sort_order=DESC&items_per_page=24&Collection=
Not sure I’m following, why do you need SetDate? I assume you mean Texture.SetData?
Use an external UI lib (disclaimer: I wrote one). You can find some options here:
But if you prefer to write yourself please provide more info because I didn’t quite understand what you meant with the SetData thing 
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