Can anyone tell me if there's a websight where I can source building plans for a house built in Wallasey in 1901?

Out of curiousity what is the street name? I appreciate you can't give the house number.

I don't know that you would be able to do so. It'll be registered so chances are any old deeds will have been destroyed. (floor plans don't count as deeds so you prob wouldn't find one even if you had the old deeds).

Wirral Archives have copies of building plans for Wallasey dating back to the 1870s; they don't have a complete set but it's possible the one you're after may have survived. If you email a request to them, giving as many details as you can, at [email protected] they should be able to look for it for you, and if it still exists provide you with a copy, either hard-copy or by email, for a small charge.