Currently I am working with a project, where my goal is to real time map updates for AD through RGB-d video feed. The problem I am facing is with the creation of the base map which will be updated later. I have been researching techniques to build a HD map from laser scan data and fusing other sources like road networks. I haven’t found a clear step by step method to do so yet. There’s a lot of file formats, tools for different tasks which is very overwhelming for me.
I have this laser scan data of the region where I will be doing the experiments. Here is the metadata:

The laser scan data was downloaded from https://asiointi.maanmittauslaitos.fi/karttapaikka/tiedostopalvelu/laserkeilausaineisto_05?lang=en

Coordinate system etrs-tm35fin

Scanning date 2023-06-12

Elevation precision (m) 0.1 m

Elevation system N2000

Flight altitude (m) 1475 m

File format LAZ

Updated 2023-10-12T05:50:00.276458Z

Map sheet number R4412H4

Point cloud identifier laser/automaattinen/2023/20230206_Swissphoto_Oulu_kesa/Harvennettu/R4412H4

Point density (points per m²) 0.5 pistetta/m2

Project(s) 20230206_Swissphoto_Oulu_kesa

Scanner Riegl, VQ780IIS

Scanning timeframe C

Year of scanning 2023

I have two sources from where I can get the roads and topography:

https://www.openstreetmap.org/

other one is from the same website I got the laser scan from, but this data is a bit different:
https://www.maanmittauslaitos.fi/en/maps-and-spatial-data/datasets-and-interfaces/product-descriptions/topographic-map-series-raster

I am confusing how do I create the HD map from this data! What other data I need to build a good HD map?

Please provide me with some guidance.