hi....is there anyone who can give me some ideas to scratch build a small bridge?

Stone or wood? Stone you can use cork over a foam board base, wood you can just do a timber bridge with a flat deck.

Look at this for a start on wood
Die Pressung

the bridge is going to be stone.

Here is one nice quick cork feature
Cork Just use it vertically and in stone sizes vs. brick sizes.

Here is a bridge Bridge