Fingal - Plot size V footprint size

[melon]

Am waiting to get hold of someone in Fingal but have a query ..looking at a 0.1 acre (1/10 acre) plat in fingal 100ft long by 50ft wide approx...houses around it are all dormer /bungalows..Just wondeing if there a general rule as to what size the bungalow could be ie would we have to leave 2000 sq ft foor garden , front etc... Just trying to acertain if we could build a 200sq ft house in it (planning permission obviously needed) as if there is guide that says we could only build 1400 then wouldnt investigate any further...