Suggestions

First, set buildings dimensions and plan the surrounding area taking care of usage, loading needs, access and roads.

- Figure a dimensional plan.
- Figure the use of the building and the surrounding area.
- Figure the history for the owner and evolution of the structure.
If you freelance in some grade your RR , is important to don't waste your limited real estate with thinks that don't add interest or operational options: you're building a RR, not a diorama.

<- This is my preliminary sketch for this shop

Test your skill on simple jobs.
Sure a shed seams so simple? It depends !
It still need foundations, doors and roof:
- expertize new solution on a little building will take you to new level.

- Limit the inside details to what you can appreciate from outside

I model in N scale, so go too far with too much details is not a key point: model what the viewer can appreciate is the rule.
About inside details: what is important is to "suggest to viewers that inside is not empty". I've add just a working bench, a wall library (simple sticks of painted wood) and a calendar on the wall in front of one of the doors..

Verify twice "before"!

Test fit "before" you use glue.

Check colors of different parts.